Sparky
Check your timing chain stretch, you may need to give it more advance as it is running "late" in cam timing. As long as it does not ping don't worry about the total. You may be in need of a new chain and gear set...If anything the car may be running rich in the cruise mode-did you look at a plug or 2?

Radiators are about 249.00 on rock auto. You do not need to get stupid about buying a rad as for these cars the stock rads work fine when they are not plugged.

My technical support conclusion is the radiator.