Overheats on highway only

dont try any of the flush crap, i worked in a radiator shop for 2 years, flush is a waste of money and time, we also did what was called rodding, where you take the radiator out and take the top tank off and run a long slim piece of metal through all of the tubes inside the radiator, was a cheaper route but took a lil longer then just replacing the radiator

I had freeway running hot issues on my 1988 Cab Plus, replaced radiator with a 2-row radiator (such as the automatic transmission models had) and no more running hot (Arizona, AC)