Reverse cooling

BB Mopar engines aren't designed for reverse cooling so you're fighting a loosing battle from day one. If you're interested in making more power then reverse cooling is just a time sink. Spend your time working on the intake manifold or cylinder heads and you'll have more to show for it.

On your engine all you need to do is reverse the direction of the hoses and you'll be back to conventional cooling. Try that and see if your problem goes away. If it does you have your answer.