Over heating

If the engine overheated, it had nothing to do with your AC system. I would suspect that you have a failing fan clutch, especially if it overheats at slower speeds. At highway speeds, enough air will pass through to cool the engine.
ON your AC system, you have two electric fans that will come on to cool the condensing coil. These fans have a very nominal affect on engine cooling but do affect your AC, especially if the fan clutch is failing which will draw air through the condensing coil.
You said that you added coolant after you pulled over. That would indicate that your radiator boiled over and you lost coolant. Just adding coolant is one thing but unless you PURGED all of the air out of your cooling system, you could still have cooling problems due to cavitation of the water pump caused by an air pocket.

I have had my A/C on going in and out of all the grades in Calif. and never has it effected my engine temperature. I think I would keep looking for the culprit.
Just my 2c.

Yes I always carry a couple of gallons of Dex-cool. Drove an additional 180 miles with the only difference being the a/c was turned off and had no problems. I'm going with it was the a/c. Thanks!

The first thing I would consider is what's in it. Has it ever had the coolant changed? Has it had a thermostat? Is it dexcool? Doesn't really matter now but what type of coolant did you add?

LOL. Ideas? How about a clogged cooling system, colapsed radiator hose, frozen AC compresosor, fan failure. That is just for starters.