l changed the heater core,thermostat,radaitor cap,raditor flush,new water pump,its still over heating

When is it overheating? Within minutes? On the highway?
Check timing, stuck egr valve, if it is running lean, missing air dam, etc.

Why would you change the heater core?

head gasket, but bring it to your mechanic or a dodge dealership.

blown head gasket.especially if you are getting white smoke..

or if it is running rough..slipped timing chain..

if the timing is to far advanced it will run a little hotter than it should ,you might want to check that and also check to see if it is building up a lot of pressure under the cap,if its above normal you may have a blown head gasket on it they will run good but run to hot when one blows,i drove my truck for month before l could actually pin point that it had a blown one on it,because it never gave any of the normal symptoms that a head gasket usually gives,good luck.