Was the new thermostat OEM?? If not, I would pull it out and check it per the manual. Actually, even if it is OEM I would pull it out. Sounds like it may be sticking in the closed position.
I'm assuming you used the correct size tubing when you relocated the radiator?
Did you bleed the system well after you relocated, refilled the radiator and reserve tank? Air in the system will cause overheating.