It finally occurred to me why I didn't have much hot water or water just barely above warm. I'm operating it on propane and the propane side (12v) thermostat was failing. I keep spares for both the 12v and the 120v thermostats so I replaced the bad 12v one. Problem solved and then took a hot shower. Life is good.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof