Thanks guys, getting rid of some carbon build up did seem to help a lot, but I haven't driven her under load when at full operating temp yet.
Bill, I think you're right with the rear gear ratio, that does seem to ring a bell. I am almost certain that the 318 is bone stock, so you could be right. I think I'll try lead additive next time I fill up. The engine is always right in the middle of the gauge, which I assumed was right. I have put in a new 180* (I believe it was 180*) thermostat. After I kill the engine, if it is warm, and I let it sit for a few minutes, and turn the key back into ON, the gauge will read much higher, sometimes (rarely) near the top of operating range. I assumed that this was due to the really hot cylinder walls and heads spreading out their heat after there's no more coolant flow. Because of this I have started to let the car "cool down" by idling for a short while after high load driving (I live on the top of a pretty tall, steep hill with many curves). The car does have electronic ignition, which I'm grateful for because I would be fine to go my life without dealing with points. I can't be sure, but I am willing to bet that it's the original timing chain. Is there any tests I could do without taking off the timing cover and dealing with that can of worms? The timing chain is not going to be my next step, but I will keep it in mind. Thanks for your thoughts.