* Do a long drive and then stop car and while idling, reach down and feel the lower hose in your hand; warm, cold, hot?Thermostat I bought is bad, go get OEM part
* I somehow think the issue is not the Tstat. put old and new ones in water pan and cook them. Watch carefully to see when it start open and notice the water temperature. If they opened way before boiling (70 or 80C) then they are no good. They should start open just before boiling, around 97C.
* How did you bleed the thing, in detail steps?