Another thing is to use the bypass hose and use the proper size hose (5/8's) and proper shape (pre-formed 90 degree). I recently had a 396 over heat when I didn't use the short bypass hose going from the water pump to the intake. I put the hose on and all the over heating problems went away.
For some reason, my 454 didn't need the bypass hose to run cool. But, I would put on a hoses if you aren't using one to see if that is the problem.