I think predawn is blowing a lot of smoke in this forum. I guess he does not realize that the engineering department will install engines according to the weight of the coaches.
He claims he has the ISL 450 on his coach and can not pass trucks going faster then 70 miles per hour. LOL. Who wants to be driving up a six percent grade going 70 miles per hour anyways. But the reason why his coach can not do it is probably because it is a heavy coach, so that ISL even with the horses it has, it is still carrying a lot of weight.
So a coach that is 36'or 38' with a 350hp diesel should be perfect for its weight.
All I can say is that my coach has the 3126-E Caterpillar and I have traveled all around the country with no problems as far as power goes. First towing a Honda Pilot weight of 4200 lbs and now a Honda CRV and I can not even tell they were behind my coach. I also noticed that those Cat engines it takes about fifty thousand miles before they are broken in. I have 60K miles on the engine now and my coach is running at its best. One thing that I did notice gave my coach a lot of power was changing the air filter from a Farr to a Rancor filter. Wow! a lot of difference in power.