Did you check the computer codes?
Hard to say much without knowing why
the check engine light goes on.
Thats not a very big engine to pull an RV,
but if it's not overheating, I don't see
why the RV would be causing the problem.
Almost sounds like the engine is carboned
up...If it's got carbon around intake valves,
it can keep them from fully closing when the
carbon gets real hot and expands..Might run
some techron or whatever for a while to try
to clean up any carbon..That carbon problem is
real common with toyota's, etc..But I imagine
applies to most all fuel injected cars..
MK