We put over 100,000 miles on our 2001 (310 hp) before trading it in on a 2013 (362hp) earlier this year. We never had an engine problem. We towed either a Buick Le Sabre on a dolly or a Jeep down for about 98,000 of the motorhome miles.
The only time we had a problem with power was when the fuel filter got plugged up. When it finally dawned on me what the problem was it took about 10 minutes to resolve it. The old filter was so plugged up it weighed about 5 lbs. Once it was changed out it ran just like it was supposed to.
We now have a 2013 (362 hp) it does have more power than the 2001, but the older one was more than adequate. The new one already has been to Alaska and back (11,000 miles towing the Jeep)and it's just getting broken it.