[MRDeadhead]

Here's the lowdown. I replaced the thermostat...no difference. I replaced the radiator cap...no help. Flushed and refilled with new coolant...no help. Replaced the water pump...bingo! Apparently, when these water pumps go bad, the shaft spins inside the {plastic} impeller and it doesn't circulate the coolant. When they are cold, the shaft spins the impeller...but once it's warm, the shaft spins INSIDE the impeller since the plastic expands more than the steel shaft. Hence the feverish croozr. As for the on/off warm/cool air thru the heater, don't know about that one. The heat is fine now...can't understand how the temperature of the heater air would drop that quickly. But as long as it's working, I'm not too concerned. Now if I could only figure out why the oil pressure on my Jeep Wrangler gauge is pegged at 80 psi, I'd rest a lot easier. Thanks to all who aided in my dilemma...you're good people!