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2011 Big Three Diesel Truck Shootout: GMC HD

Posted in Project Vehicles on June 1, 2011 Comment (0)
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Photographers: David KennedyKevin McNulty

As we got to know our pickups, the GMC in many ways became the Goldilocks truck. If the Ford’s spring rates were too soft and the Ram’s too firm, the GMC’s were just right. Likewise, those who found the Ford’s dash layout too busy and the Ram’s too plain found that the GMC’s straightforward ergonomics hit the sweet spot. Stylewise, this was the case too: Ford’s grille was judged way too gaudy, the Ram’s big-rig nose a little out of date, but the GMC’s front end, like the rest of the truck, was contemporary and muscular.

That’s not to say the GMC straddled the middle ground everywhere. The only IFS truck in the bunch, it was a target for purist judges, one of whom felt it exhibited far too much body roll in corners, whether it was attached to a trailer or not. He also described his experience in a sandy wash as not as smooth as the solid-axle trucks. It was bounce-bounce-bounce through the whoops. Too much power for the suspension.

On the subject of power, GM’s 6.6L Duramax V-8 may have lost the horsepower battle to Ford on paper, but in our test the trucks were pretty much in a dead heat. Both offered plenty of grunt for pulling our trailers up even the steepest grades, and the trucks never broke a sweat while cruising the interstate, even when facing fierce headwinds. During our instrumented tests, the GMC was quickest through the quarter-mile unladen and a close second while towing. Likewise, it turned in the best fuel economy when empty and the second-best while towing.

This latest generation of the Duramax has been refined in several ways. As with all these trucks, it has been fitted with new exhaust equipment to meet stricter emissions laws. But it has also been reworked internally, with improved oiling to the main bearings and turbocharger, stronger pistons (that are lighter as well), and modified connecting rods to better support the pistons.

The new Duramax is mated to a new Allison 1000 six-speed transmission. It was strengthened to handle the Duramax’s higher torque output, but it also assists with the operation of the engine’s exhaust brake, which is actuated via a dash-mounted button. Of the three trucks, we liked the GMC’s exhaust brake the best. It came on exactly when we needed it, nicely matched the transmission when it downshifted, and stayed on until we shut it off. Not all our trucks could make that claim.

The Allison did display one trait we didn’t like: In tow/haul mode it tended to hold a gear longer than we thought it should, spinning the Duramax faster than was probably necessary. While we were climbing Montezuma Grade, for example, the Ford and Ram would be loping along at 1,500 rpmtheir torque peakwhile the Duramax was taching 2,100, far above peak torque. This wasn’t driver-specific; every one of us experienced this. Canceling tow/haul would bring on an upshift and lower the rpm, but then the Allison would hunt for a lower gear and the revs would climb again.

The GMC’s steering didn’t win much praise. Most judges felt the steering effort was too high, especially when compared to the lighter effort in the other trucks.

By the way, can someone please explain why GM can’t center its steering wheels in front of the driver? Like so many GM products, this wheel was offset slightly to the left. While we’re complaining about the GMC’s interior, we would add a grab handle on the driver-side A-pillar and move the backup camera display out of the rearview mirror, where it’s so hard to see that it took us most of a day to realize we even had a backup camera.

Back to steering. On a dry lakebed we held an impromptu turning-circle contest and confirmed what most of us believed: the GMC’s turning radius was the largest of the three. (The Ram turned tightest.)

When we left the sand and dry lakes for the rocky hillclimb portion of the test, we missed the Ford’s E-locker. The limited-slip unit in the GMC’s rear axle needs wheelspin before it’ll work, so the gnarliest, loosest spots took lots of throttle and momentum to negotiate.

Likes

  • Exhaust brake
  • On-road steering effort
  • Instrument panel layout

Dislikes

  • Agressive tow/haul gears
  • Off-road steering effort
  • Wheelspin before axle lock

View Slideshow

Specifications
General
Manufacturer GMC
Model Sierra 2500HD SLT Crew Cab 4x4
Base Price $44,560
Price as Tested $56,629
Engine
Type V-8
Displacement (L/ci) 6.6/403
Bore & Stroke (in) 4.06x3.90
Compression Ratio 16.0:1
Fuel Req./Capacity (gal) Ultralow-sulfur diesel/36
SAE Peak Horsepower 397 @ 3,000 rpm
SAE Peak Torque (lb-ft) 765 @ 1,600 rpm
Transmission
Type 6-spd auto
Ratios. First: 3.10:1; Second: 1.81:1;
Third: 1.41:1; Fourth: 1.00:1; Fifth:
0.71:1; Sixth: 0.61:1; Reverse: 4.49:1
Transfer Case
Type 2-spd, part-time
Low-Range Ratio 2.68
Axles
Front Type 914-in
Front Diff Open
Rear Type 1112-in
Rear Diff Mechanical locking
Hubs Fulltime
Ratio 3.73:1
Traction Aid Eaton mechanical locking differential (rear)
Suspension
Front Short/long-arm independent, torsion bars, shock absorbers
Rear Live axle, longitudinal leaf springs, shock absorbers
Steering
Type Power-assisted recirculating ball
Ratio 16.1:1
Wheels
Size (in) 18x8
Material Aluminum
Tires
Size LT265/70R18
Brand Michelin LTX A/T2
Brakes
Front (in) 13.97 ventilated disc
Rear (in) 14.17 ventilated disc
60-0 Unladen (ft) 147.3
60-0 Towing (ft) 214.3
Acceleration
Standing 14-mile Unladen (sec @ mph) 15.75 @ 85.49
Standing 14-mile Towing (sec @ mph) 19.83 @ 68.39
Weight (lb)
Curb Weight 7,660
Curb Weight w/ Trailer 12,620
Advertised GVWR 10,000
Tow Capacity 13,000
Payload Capacity 2,792
Mileage (mpg)
EPA Estimate N/A
As Tested Unladen 17.3
As Tested Towing 10.39
Dimensions (in)
Wheelbase 153.7
Overall Length 240.1
Overall Width 80.0
Overall Height 78.3
Min. Front Ground Clearance 9.0 (at front skidplate)

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