If you take close look - semi tractors have top-efficiency diesels with huge radiators mounted on front.
Per my observation all motorhomes are build the cheapest way possible and only bus conversions have engineered systems.
That said my vintage Prevost did overheat few times before I recore the radiator.
So yes, cooling rig engine is the issue and I tell you that when my front engine, front radiator Bounder died on 7% grade, that was not fun becouse I got vapor lock not only on carburetor, but on master cylinder as well.