I drive a '76 GMC with a 350 and an auto. It has a partially rotted 3 row full of stop leak. It has gone above 190 twice in the 2 years since i bought it, and that is with a 180 degree thermostat. The first time was when my heater hose burst and I lost all of my coolant and the second was while going up a moderatly steep grade in 100 degree weather. I sometimes hit 190 while going down the freeway at 65+ in hot weather or idling up a hill. I would check your ignition timing, 12 degrees at 700 rpm is a good place to start for almost any engine. Retarded timing can cause overheating. Also, if you don't mind having to prep your car for smog, remove most or all of your smog equiptment, that dropped my underhood like 50 degrees.