I have a C4500 Chevy Kodiak crew cab Dually, it has the same engine as the 3/4 and 1ton chevy/GMC trucks with the exception in my class of truck Chevy detunes the engine by 30 horsepower. I tow a 15,000 lb 5th wheel that I used to tow with a 1 ton chevy crew cab dually gas engine. With the first tow in the C4500 I thought I had died and gone to heaven. The torque from the diesel makes hill climbs a breeze, now mind you it's no hot rod but I'm able to do 45MPH up the same 6% grade that the 1 ton would get down to 25MPH on with the same trailer. Plus with the diesel it came equipped with an exhaust brake which makes going downhill a lot more comfortable and safer.
The 1ton without an exhaust brake I would have to use the truck and trailer brakes close to 20 times on a 21 mile 6% downhill run. In the c4500 I hit the brakes once to get the exhaust brake to engage and never get above 55MPH. The exhaust brake helps hold the speed without the need to keep hitting the brakes.