The 7.2 percent grade test was a 1,600-foot steady grade. That's 280 feet longer than the quarter-mile test we performed on the flat ground at Milan Dragway.
The trucks were only tested pulling trailers – 10,000 pounds for the three-quarter-ton gas and diesels, and 12,000 pounds for the one-ton diesels.
All trucks and trailers were completely on the grade and stationary before each run. All the tests were performed “brake-to-accelerator,” meaning the foot brake was fully depressed with the right foot, which then lifted and fully depressed the accelerator pedal in one movement. Sufficient distance was provided at the end (after the 1,600-foot mark) to slow the rigs down to a safe speed before reaching the top of the hill.
At least three runs were carried out in each truck, with the same driver behind the wheel running at wide open throttle in two-wheel drive. Stability and traction control were turned on in the Ford and GM trucks; Ram pickups don’t offer stability control. Tow/haul mode was enabled in all trucks.
The fastest run for each truck is included in the results below.
Three-Quarter-Ton Gas Trucks Towing 10,000-Pound Trailer
A new feature that’s available for both the Ford and GM HD trucks is hill-hold assist. Originally conceived to help vehicles with manual transmissions start out on steep hills without needing to use the parking brake or put extra wear on the clutch, hill-hold assist automatically applies the vehicle's brakes for 1.5 seconds to 2.5 seconds (depending on manufacturer) once you lift your foot off the brake when you're on an incline that’s at least 5 percent. It's also part of the trucks’ integrated trailer brake controllers, so it will apply the trailer's brakes, too, if it has electric brakes.
While Ford and GM no longer offer manual transmissions for their HD pickups, we still found the feature useful starting the hill climb from a full stop with both truck and trailer on the grade – when it worked. It didn’t on the GM pickups, which was traced back to a glitch in the hill-hold assist calibrations on the 7.2 percent grade only. That issue has already been fixed in production.
Adding gravity made the contest much more interesting for the gas trucks. When you look at the performance numbers and truck specs, there's some high drama happening among these haulers.
The Ford F-250 and Ram 2500 were neck and neck through the first quarter of the hill climb. At the 400-foot mark, they were within 1 mph of each other. As the Ram upshifted into second gear, its awesome Hemi V-8 wasn’t enough to make up for the large step between cogs. It seemed to flat-line in performance. That gave the Silverado the opening it needed to finish close in performance to the F-250, pushing the Ram to third.
Whether by design or by nature, we really liked the way the Ford 6.2-liter seemed to come to life on the hill. It sounded great in the Super Duty, as if we were driving a high-horsepower Mustang at the dragstrip.
Three-Quarter-Ton Diesel Trucks Towing 10,000-Pound Trailer
The Ford and GM diesels dominated on the 7 percent climb. It was an awesome display of greater firepower and six-speed flexibility that put the Power Stroke and Duramax rigs onto a different playing field altogether. Not even the Cummins’ earlier peak torque – at 100 rpm lower than the Ford and GM trucks – gave it an advantage.
By the end of the grade, the Silverado 2500 was 5.8 mph and 3.4 seconds faster than the Ram, and it was 1.9 mph and 1.8 seconds quicker than the Ford.
The Ram may have the advantage of not requiring urea for its diesel engine, but we think many diesel owners would gladly trade that maintenance item for the huge advantage in performance.
However, we can’t forget to point out that the well-equipped Ram is almost $8,000 cheaper than the Ford and Chevy trucks. Certainly for that bargain price, and with its handsome interior and exterior styling, we could be persuaded to opt for the Ram. So what if you don’t get to the top of the hill the quickest?
One-Ton Diesel Trucks Towing 12,000-Pound Trailer
The fastest one-ton truck up the hill was the Ford F-350, just a tenth of a second faster than the GMC Sierra Denali 3500HD and 3.7 seconds faster than the Ram.
While the Ford F-350 consistently shifted all the way up to fourth gear at least 100 feet before the end of the run, the Sierra Denali and Ram only made it to third gear. The Ford shifted into fourth at 3,200 rpm while the Denali hung onto third, just over 3,000 rpm. The Ram, which ended the run at 46 mph, was at around 2,700 rpm.
We think the F-350’s shifting into fourth gear so quickly on the grade is one part of Ford’s fuel economy strategy, to return up to 20 percent better fuel economy than the Super Duty used to get with the 2008-10 6.4-liter Power Stroke diesel.
Torque-converter lockup strategies were also interesting to observe. A torque-converter lockup clutch is an automatic mechanism that helps match engine and transmission speeds during acceleration for improved shifting efficiency and fuel economy. As we ran up the hill, engine rpm in all the trucks would steadily climb and then fall back slightly as their torque converters slipped. The Ford locked up in third gear, just before fourth and the Denali locked up in second gear, just before third. We couldn’t tell when the torque converter locked up in the Ram.
While the Sierra Denali’s launches were always clean, the upshift from second to third was consistently a bit harsh. The Ford exhibited some rear-wheel hop, even though it was a dually with 12,000 pounds hanging off its bumper.
We noticed interesting transmission temperature variations among the three trucks. The GM trucks typically had the lowest temps, from 174 to 196 degrees; the Ford Super Dutys consistently stayed within a remarkably tight band, from 196 to 198 degrees; and the Ram pickups ran the hottest and climbed in temperature the fastest, from 178 to 208 degrees.