"Flushing" a radiator rarely solves such problem. MOst often very thin mineral deposits from hard make-up water impair heat transfer and this does not go with a "flush".
Make sure there is no external clogging at A/C radiator from vegetation . Also, make sure fans work specially if A/C is used at idle. I kind of understand the problem alleviates or disappears when running at highway speeds and this rules out engine problems.....
TO remove radiator requires detaching the dogbone at radiator and swing rearward. then, as the book says:
- remove forward lamp harness from fan frame and unplug fan connecetor
- remove fan attaching bolts
- remove fan and frame assembly
- remove hoodlatch (mark position to ease reinstallation)
- remove coolant hoses, transaxle coolant lines and radiator support bolts
- remove radiator.