I have a 2002 dodge truck that just began over heating. I checked thermostat and it works, I replaced water pump, flushed radiator and heater core, replaced radiator cap,bled air from the radiator, and it still over heats. The curious thing is it only over heats when you have the transmission engaed, driving. At idle it will never over heat. Any suggestions?

Sell it for scrap mine was same year and model did the same it's a model flaw just get rid of it a ford ranger 2002 does the same as well

Replace the radiator. Internal passages may be blocked by phosphate scale. Afterwards, refill with a 50/50 mix of the proper antifreeze and distilled water.