Yes the DP will out pull a gasser, all day long. It will not even break a sweat, so will a gasser, with a sweat.
We had a 17,000lb Class A and with our toad behind it, with a gear venders under/overdrive and on good grades the rpms on our gasser would be 3000rpm where Our current DP can do it without a thought, at 1700rpms. That's with the same toad, and our DP is about 10,000 lbs. heaver/ When we pulled the toad with our gasser our fuel milage was about 6 mpg compared to our DP which is about 12 mpg.
Gettimg up grades takes torque not rpms, gas engine cannot conpare torque with deisel
In conclusion with our gasser we poke along up the hills, with the DP going up the same hills was like riding in the flatlands. we still like to poke along, now it's by choice!