I have a deposit down on a 1997 Itasca Class A 32'motorhome with a 460 Ford V8. Currently I have a 1990 E350 27' Class C, also with the 460 V8. Here is the interesting part: The E350's 460 calls for 5w30 or 10w30 PCMO, but the Class A's 460 calls for 5w30 or 15w40 HDMO (specifically says rated CF4). So I am both excited and dissapointed at the same time. I am excited that I can run Valvoline Premium Blue 15w40 in it, but I am dissapointed because my 160 quart oil stash has absolutely no HDMO. Ah well, I probably can just beef up the PCMO with SLOB or some other additive. As for the big difference in oil spec, I can say the Class C is 9500 lb dry weight, whereas the Class A is 13000 lb dry and has a larger load capacity than the Class C. The Class C's 460 runs 65 psi hot on 10w30, so I could not imagine running 15w40, but maybe the Class A's 460 is built different. Perhaps the oil pump is different. It will definitely work harder with the extra lbs.