As an engineer (retired) I'm always amused by the arguments over diesel vs gas torque. The interesting part is that your diesel, generating 800 ft lbs at 1500 RPM, is exactly equivalent to your gasser generating 400 ft lbs at 3000 RPM. Why? Because both engines drive the same size wheels but at different engine speeds, so the gasser has a final gear ratio which is 2X that of the diesel. Guess what the 2:1 gear ratio does?- it multiplies the gasser's engine torque by a factor of 2. So, at the rear wheels, both engines provide the SAME torque.
now to be fair, the diesel is humming in the rear of the coach, while the gas engine is roaring under your feet.
This discussion always reminds me of the specifications for the M1A1 Abrams tank. 135,000 lbs, top speed of 60 mph, able to climb 45% slopes! And all with 270 ft lbs of torque!
How do they do that? They generate the torque at 30,000 RPM, then feed it into a 10:1 reduction gear. So then you've got 2700 ft lbs and 1500 HP at 3000 RPM.