rear heat blows cold

[jrn2786]

I'm sure this subject has been beat to death, but my searches has turned up with no helpful results. So I have a 99 5.4 xlt. Rear heat acts like its gonna bkow warm for a second or 2 then gets cold. front heat leaves somthing to be desired but still fairly warm. Rear heater core gets hot as well as both lines. Both doors are workingroup properly. My scan gauge read 185-190 degrees coolant temp. I have no idea what the issue would be. Is it possible the thermostat is sticking open? I wouldn't think 5 degrees less would make that kind of difference. I'm kinda lost