In the last few days we have noticed our RR wasnt blowing hot air. Last night it overheated. This morning we topped off the coolant level and started it. It ran fine, no hot air in heater...then it began to overheat again. Of the two hoses running to the heater thru the firewall only one was hot, and really hot. The other was warm, also the radiator hose was extremely hot. We could find no antifreeze leak at all... Heater core???

 

From the description of the hoses, I would say either you have a blocked heater core,a leaking heater core, leaking heater core o-rings, a leak that you just haven't found yet, or a combination of all three. Is your passenger side carpet wet? Have the system pressure tested and see what you come up with.