ET2, your pickup truck, towin any currently manufactured fiver, did not weigh 43,000 pounds! Not even close.
It gets confusing these days with the pickup truck motor's HP rating overlapping the cummins ISC 8.3 liter...
The 8.3 has one thousand fifty foot pounds of torque. This is computer limited due to the rating of the Allison MD3000 transmission (the engine can actually put out much more)
These engines were rated anywhere from 300 to 380 HP, depending on application, always with that same 1050 torque rating.
Ours, a 360, struggles some up the big passes in the west, down to second gear and 40mph sometimes.
After having driven a v10 gasser over these same "hills" at 20 mph, 5500 rpm, in first, I just thank my lucky stars for that big ISC.
While Fleetwood must know what they are doing putting the ISB in the 34 and 36' versions of this motorhome, I personally would get the forty footer just to get the bigger engine.