A little background first: I have a '78 P30 Itasca class A motorhome with a 454, th400, and 4.56 gears with 235 85R16 tires. Currently the 454 runs like a top and I really have no complaints other than when I am towing a trailer with a couple ATV's on it or pulling my enclosed fish house trailer into a good headwind the 454 likes to run a little hot. I have had the radiator flushed and put a high flow 180 degree thermostat in it and that helped some, but I have to keep my foot out of it when pulling. Oh and when towing into the wind like that, its a 5 mpg adventure. I have been entertaining a 12V Cummins swap bolted to the TH400 with a Gear Vendors OD unit and probably re-gearing to 4.11's. The cost and complexity of that swap (along with the added weight to a already taxed front suspension with air bags) makes me wonder about other possibilities. First thing I could consider (and probably will be what I do) is look for a new aluminum radiator to help with cooling the 454. The other option I have been kicking around is finding an early mechanical 6.5 Turbo. I have had some people tell me that they can be retro fitted with the newer cooling updates and can be made reliable. I'm curious if anyone here has experience with 6.5's. I had a '97 K2500 with a 6.5 and it was a pretty decent pickup other than it would heat if towing in the hills. I like the idea of a 6.5 because it would be easier to bolt in, and weigh less than a Cummins, and should get better fuel economy than the 454. The biggest concern I have is keeping it cool because the motorhome alone weighs somewheres in the neighborhood of 11,000 pounds I think and it has the aerodynamics of a barn door. So, long story longer....would a 6.5 Turbo even be something I should consider?