Re: Overheating...need advice
You answered your own question kinda. You know what is possibly going on you just are a little stumped. Make sure stat is installed correctly, and that the lower rad hose isn't plugged. Verify correct rotation of water pump/correct rotation style pump. They have reverse rotation pumps.
I would drain it, pull the stat, inspect the hose, blow thru the rad, run water thru the rad, run water bacwards thru the stat outlet flange,leave the stat hsg off, slowly fill the system until I had water at the stat, pull the belt and manually spin the pump to flow check, put the stat/top hose and fill full, run with cap off and check for flow.
Hope that helps. It's what I'd do if I walked into it cold anyway with your symptoms. Easy to do.