[69gmcc10]

There could still be a air bubble in the system. Was there a vent hole in the T-stat? I always try to buy a T-stat that has the little vent hole in it or drill a small hole in the base plate of it to help minimize air getting trapped.

Get an IR temp gun and check the temp at the sensor in the radiator (top, bottom and middle) to see if the temp sensor is accurateish and if there is a blockage in rad. With enough tinkering you will get it figured out. good luck!