I find it interesting that the OP"s motor home is a 2002. Something has obviously changed. Too bad he did not provide more info such as how long he has been experiencing the problem and exactly what has been done trying to fix the problem. I cannot believe a repair facility charging $5k and not being able to identify and fix the problem. If the engine overheats within a mile or so, there has to be absolutely no coolant flow through the block of the engine. Will be interesting if the OP reports back when the problem is eventually solved.
Ray