Welcome to CHR. Running 55-75 cruising you should be at your thermostat control temperature if everything is right - no air bubbles in the system blocking flow, enough radiator volume, good water pump, no air flow restrictions, etc. Where is your sending unit located for your gauge giving you the 220F at cruise? What's the setup in the car? In mine (not a hemi) I found that my temp in the water jacket by the heads (ECU input) ran ten to twenty degrees hotter than my dash indicator measuring at the water neck, so I backed my T-stat down from 195 to 180 and reset my fan controller using ECU temps and it's been fine. 220F is not going to hurt the hemi, but I would be concerned with it being that high at cruise - you don't have much cushion left.