Were you able to take temperature readings as suggested in
this your post?
Make sure you installed the correct thermostat type. Should have the bypass blocking plate like this one:
Example photo.jpg
Otherwise too much coolant will just recycle thru the engine and never make it to/from the radiator. Same problem with running this engine with no thermostat. Overheat.
The bypass design is supposed to equalize engine temps (hot spots) and allow early heater before engine reaching operating temps.