When we were shopping to make the move from 5th wheel to motor home, we compared a new Tiffin 36TLA gas coach (Ford V10) vs used Tiffin Allegro Bay 38QDB FRED (6.7L Cummins) vs used DPs (Cat C7 and 6.7L Cummins). Here in Florida's flat lands, all four engines seemed to move the coaches with ease, I'm not a major throttle jockey and as I said...no hills.
Ride wise, the Gas and FRED rode about the same, I'd give the nod to the FRED due to the heavier Freightliner chassis. The DPs both had air ride, so they both rode nicer than the Gas or FRED. For me the choice boiled down to braking. The Gasser brakes scared me, I can't imagine driving the V10 in mountains. Little to no engine braking, so all you have is four small disc brakes, to slow that beast down. The FRED has diesel engine braking and larger chassis brakes. Again the nod goes to the FRED.
In the end we purchased a used DP. You just get more for your money. Granted it's older and there is more to go wrong, but the ride and extra's just made it worth it for us. Ask me again in 4 years....when the extended warranty runs out.Go to the full post