Okay, I read just about everything on the forums....check this out, overheats when thermostat is in, doesn't even get in to the normal temp range when it's out. I tested the thermostat in boiling water, it works fine. The fan comes on just fine. The radiator is a normal temp on both sides and no coolant leaks anywhere. The radiator was flushed with a garden hose and it flowed fine. Block was also flushed and the system was Burped.

Maybe one of the upper and lower rad hoses are colasping, Could have little bit of blackage in youre rad cores, Plugged Heater core, Leaking H/G.