What specific problems are you having?
My Onan 12.5 genset in my 2003 Lexa would overheat, but only on very hot days (> 100), travelling fast, with all 3 rooftop AC on.
Things improved substantially with a good cleaning of the radiator, a new thermostat and coolant replacement (it hadn't been that long) made no more improvement, but it still ran hot in such conditions. As soon as I stopped driving (rest stop, etc.), temps would drop fairly quickly, so it was clearly related to traveling - my theory is that low pressure develops on the front (radiator intake) side, reducing overall airflow volume.
My solution is to never run all 3 rooftop AC when traveling - two is plenty, and if I stop and it's warm in one of the zones, it's ok to turn on the third. though it might take a little bit longer to cool off the coach at the start of a trip if it's been parked at 100+.
A related issue is that though the OTR AC is still blowing cold it's noticibly weaker in recent years, vs the 40,000+btu of cooling I should be getting between from the front and rear evaporator zones. Once I service (on my list), I'm sure it'll be blasting cold air and I'll perhaps not need to run overhead air at all even at 100+.