Since the radiator clutch and fan are all new here is where I would start, I'd check all the hoses make sure none of them are kinked or collapsed. Check the coolant level, bypass the heater core maybe its clogged or restricted in some way. Check the thermostat make sure its operating properly. I had one that had I had rigged up with an improper hose and it was was kinda on wonky, when it would get warm I guess it was in such a bind in would collapse and I would have temp problems I replaced all the hoses with the flexible hose and it solved it. That was in a slant six. Ita worth a look see! The heater core is a good possibility too.
