For 2008, Dodge Ram heavy-duty line gets a new model, the SXT which slots between the ST and SLT lines.Also updated are woodgrain trim (dark maple burl), electric-switch 4WD on SLT and higher trim, tire pressure monitors on single-rear wheel models, and a slight increase in maximum weight for the largest models.

The Dodge Ram Mega Cab was launched as a 2006 model.Mega Cab is built on the Heavy Duty chassis and comes fitted with the Hemi engine.The extra-large Mega cab was created by re-proportioning the relationship between cab and bed on a long wheelbase truck, adding 20 inches to the cab and shortening the bed to 6 feet, three inches.

The result is acres of cab space, with six seats and plenty of head, shoulder, leg and hip room.The Mega Cab is aptly named.The back seats are roomy and comfortable with reclining seatbacks, separate rear heating and air conditioning outlets, reading lights and a center armrest with cup holders, and available DVD entertainment.there's space behind the back seats for cargo.Folding down the back seats reveals a huge cargo area (more than 70 cubic feet) with a flat load floor.The rear doors open big and wide, making it easy to load stuff inside.Covered bins are provided back there for storing gear and smaller items, and hooks are provided for hanging things.

The Ram Mega Cab rides and drives like a heavy duty pickup, regardless of the 1500, 2500, or 3500 rating, and it doesn't make sense unless you're towing heavy loads or have a big work crew.

We found the Dodge Ram Cummins turbo diesel quiet, powerful and responsive.The exhaust brake provides engine braking down long highway grades, thereby leaving the brakes cool, fade-free, and ready for stopping.The diesel's power and fuel economy make it an excellent choice for owners who tow heavy trailers long distances.

The Ram Heavy Duty models are equally at home serving solo contractors, landscape crews or families with heavy toys, and everyone in between.Despite a reputation for being the most truck-like, the heavy-duty Rams are civilized and make trucking enjoyable.

The Mega Cab 1500 is the light-duty configuration, but still has the heavy parts underneath and can haul payloads of up to 2,430 pounds and trailers of up to 8,750 pounds when equipped with 4.10:1 axle gears.The Mega Cab 1500 comes with the 5.7-liter Hemi V8 and a five-speed automatic transmission, and prices range from SLT 4x2 ($32,735) to the Laramie 4x4 ($40,325).

The 2500 ($26,140-$42,410) comes standard with the Hemi V8 with six-speed manual or available five-speed automatic, optional with the Cummins 6.7-liter Turbo Diesel (about $7,100) and a six speed manual or six-speed automatic.The Power Wagon is $37,950-$41,185 depending on cab, and 4WD adds about $3,000 to any standard 2500-series.

The 3500 ($28,345-$49,920) may appear pricey because the Cummins diesel is often standard equipment, especially on dual rear wheel models.Engine and transmissions are similar to 2500 models, though the Hemi doesn't rev as much and is detuned to 330 hp.

For adding your own box or work platform, Chassis Cab models are offered in regular and Quad cab versions of 2500 and 3500-series trucks, starting at $21,940.

ST models are workhorses, with standard vinyl floor and upholstery, although they do include chrome bumpers and grille outline, air conditioning, ABS, CD player, intermittent wipers, sliding sun visors, a full-size spare, and tinted glass.Options are limited to powertrain and chassis equipment, side curtain airbags, and a few cosmetic upgrades.

SXT adds a bit more bright trim and chrome, including the wheels, power mirrors/windows/locks, cruise control, remote keyless entry, carpet, and cloth upholstery.A TRX4 Off-Road package may be added, consisting of aluminum wheels and more aggressive tires, limited-slip differential, skid plates, tow hooks, fog lamps, and unique shocks.

SLT, the standard trim on Mega Cabs, includes an overhead console, speed control, power windows and door locks, keyless entry, and power mirrors.Options for SLT include a power-sliding rear window, a bed liner, powered trailer tow mirrors, sun roof, power adjustable pedals and driver seat, AM/FM/6CD/MP3 with Infinity speaker, navigation, Sirius satellite radio, DVD rear-seat entertainment system, UConnect Bluetooth hands-free wireless communication system, bucket seats, YES Essentials stain-repellent cloth upholstery, and 17-inch forged aluminum wheels.A part-time electric shift transfer case is available on 4WD models.

Laramie models add leather upholstery, dual-zone climate control, steering-wheel-mounted audio controls, heated front seats, security alarm, auto-dimming rearview mirror, chrome moldings and Sentry Key engine immobilizer.Options on the Laramie package include an entertainment system, sun roof, bucket seats, Bluetooth, and the navigation radio.

The 2500 Power Wagon comes with the Hemi only, electric-locking front and rear differentials, disconnecting front sway bar, Warn 12,000-lb winch, and 32-inch BFGoodrich off-road tires.It can be outfitted with leather, sunroof, DVD entertainment, and towing mirrors, among other items.

Safety features include dual front multi-stage airbags, three-point belts in all seating positions with constant-force retractors, LATCH child-seat anchors, child-protection rear door locks, and four-wheel anti-lock brakes.Side-curtain airbags for front and rear seats are optional ($490).

From the side, the Mega Cab makes an even more dramatic impression.Very wide rear doors are unique to the immense Mega Cab, with a very large proportion of window glass to door.The dark glass rear doors and wide pillar suggest a limousine, and interior volume reinforces the impression.Behind this huge cab, the bed looks small, but it remains significantly large: 6 feet, 3 inches in length and 51 inches wide between the wheel wells.There is no factory long-bed Mega Cab so use a sliding hitch for your fifth-wheel.

Long-bed Ram dually models have fender flares that look tacked on but are often cheaper to repair after impact, compared with the more integrated designs from Chevy, GMC, and Ford.

Mega Cab and Quad Cab interior space is nearly identical with the exception of rear legroom.The Mega Cab adds some 22 inches of cab length to the already-wide interior, taking second-row spaciousness beyond any previous production pickup.The Mega Cab's rear seats offer 44.2 inches of legroom, compared with 36.7 inches for a Quad Cab.And there is room for the rear seats to recline, tilting up to 37-degrees for added comfort.The rear seats also have their own reading lights and a center armrest with cup holders, plus separate rear air conditioning and heat outlets.

DVD entertainment for rear seat passengers is available, with wireless headsets and integrated game ports.Behind the passengers is a power sliding rear window for flow-through ventilation.Because of the added length of the second-row seating area, the air bag system had to be redesigned with larger side curtain air bags.Each side air bag has its own impact sensor in order to trigger the air bag on the side where impact occurs.

From the driver's seat, the view is of a wide center stack with large knobs and buttons, precisely finished with consistent angles and cut lines throughout.The instrument panel cluster is located under a prominent dash brow to reduce glare and improve visibility of six white-faced gauges, the latter numbered on diesel-engine models.A substantial four-spoke steering wheel houses cruise control buttons and available stereo controls.Rectangular, slat-type air vents close flush.

Interior trim is markedly different among the trim levels.In ST trim, the dash is textured plastic with synthetic-look inserts on the SLT.The Laramie package makes extensive use of woodgrain trim inside, with less plastic, for a more distinctive appearance.

The seats are generously padded and we found them to be comfortable, especially the six-way driver's seat in the Laramie, which can be shifted around as any particular position becomes tiresome on long trips.The leather upholstery adds a rich appearance to the interior of Laramie models.With the optional front bucket seats, a new center console extends from the dashboard.Bench seat models still have a shallow floor console which may not be comfortable for the center rider.

Everything about the Ram is full size.Even those of us used to operating domestic pickups and tow vehicles are aware of the Ram's imposing size and stance.Inside the cabin, it is a long reach to hand something across the console to a passenger, and there would be no hope of leaning across to open the passenger door, or grab something from the opposite door pocket.Interior door handles are large and heavily built, consistent with the large size of the Ram doors.

The cabin is loaded with nicely sized trays, slots and pockets.It seemed there was always a safe place to put something down, yet keep it within easy reach.The armrest opens in two parts and center console is big enough for a laptop, and is designed with fold-down dividers.

The navigation screen, measuring 5.8 inches, is surrounded by buttons and knobs; perhaps a bit on the small side but located up high for good viewing.With the standard front bench seat, a very wide center console flips up to allow makeshift center seating.There is additional storage under the front seat.

Power outlets are provided for the front seats.The dash power outlet is ignition switched, while the cigar lighter is always on, so we used it to charge a cell phone.A third outlet is available in the center console.

Testing the rear seat was a defining moment.One passenger, six-feet, three-inches tall, had no problem stretching out completely with the rear seats reclined.A rear-seat passenger spent an entire day with us, and declined to move up front at the halfway point.It takes a while to cool on hot days as the rear AC vents are just above floor level; adding heavier tint may be wise i.

Parking a truck as big as a Mega Cab requires some care and attention.We found it necessary to execute three-point turns into most parking spaces and sometimes to get out and look to check our final position.This, even with a very quick 2.75-turn steering ratio that helps maneuvering at low speeds, and you'll maneuver often with 50 feet needed for a U-turn, a condition not unique to the Ram.

The steering has been improved on all Rams.The 2WD Mega Cab comes with rack-and-pinion steering, while 4WD models come with a recirculating ball system.We found a minimum of bump steer and relatively precise tracking, not easy to engineer on a tall 4x4.

We noticed right away that the use of laminated front window glass and re-designed door seals has cut down on wind noise, inherent in big pickups with wide mirrors.The interior is remarkably quiet, even as we ran the air conditioning, which offers minimal fan noise on the lower settings.With any pickup, especially a 4x4, a certain amount of noise and vibration is to be expected.

We were quite comfortable in an all-day drive in a Laramie model through Virginia.With the heavier spring package that comes on dual-wheel 3500 models, we noticed some vibration leaking through to the cabin as we passed over rough railroad tracks and bridged creek crossings, but overall, found the chassis to be well damped, with a nice balance between the opposing priorities of comfort, control, and load-bearing capability.As a general rule, the more weight a heavy-duty pickup carries, the more the ride improves.

The 5.7-liter Hemi V8 is EPA-rated at 13/17 mpg City/Highway in the 1500 (2500-and-higher models are not rated) and any real-world mileage in the teens is doing well.The Hemi is an overhead-valve, pushrod V8, with a cast-iron block and hemispherical combustion chambers.It develops 345 horsepower at 5400 rpm and like any good truck engine, it makes more torque than horsepower, delivering 375 pound-feet at 4200 rpm.

The vaunted Cummins Turbo Diesel was enlarged to 6.7 liters for 2007, meets 2010 emissions requirements and has an exhaust brake as standard.The option price is listed at $6,100 but it requires an Ultra Clean Diesel charge of $995, making it about the same price as Ford and GM diesel options.Unlike the GM the Cummins comes with a six-speed manual, and unlike Ford the new automatic is a six-speed unit.Neither Ford nor GM offer the exhaust brake that makes intermountain towing stress free by delivering up to 190 braking horsepower (bhp) to control descent speed, thereby leaving the service brakes cool and free for more immediate stopping.

The Cummins is an inline six-cylinder built like a tractor-trailer engine, with exceptional longevity and low-end grunt, and it's frequently used in trucks and motorhomes that carry 2-10 times what a Ram pickup will.With the latest injection system, it is very clean (the tailpipe won't even go dark), much quieter (you won't hear it with the stereo on), more responsive, and more powerful.With either transmission it makes 350 hp at 3000 rpm, in the same neighborhood as Ford (350) and GM (365).Torque with the standard manual gearbox is 610 lb-ft at just 1400 rpm; with the automatic it rises to 650 lb-ft at 1500 rpm.Torque is what gets a load in motion, and with the Cummins making as much torque when you let the clutch out as the Hemi does at 4,000 rpm, it is the obvious choice.Many RVers report better fuel mileage towing 10,000 pounds with their Cummins than a Hemi gets in an empty truck.

Top tow rating with the Hemi is in.

NewCarTestDrive.com correspondent John Stewart filed this report from Manassas, Virginia.NCTD.com editor Mitch McCullough and correspondent G.R.Whale contributed to this report.