We're definitely on to something there. I've wondered about the slit head gaskets too but iirc people have said they are OK for the most part. But we certainly have a restricted flow for some reason that has to be what is causing this. can you post a larger pic that shows all the holes from front to rear? (to try & get an idea if the total/overall restriction is somewhere other than the gaskets). I have a good cooling mod read for you on circle track chat, a subset from moparchat (VERY informative) that relates directly to this but one thing at a time.