Overheating issue

I have never had a problem with this car until this weekend. I took it on a trip from Oregon to Santa Rosa when I went down I left at night and had no issues. I also did not use cruise control on the way down and took the 505 route. Now on the way back I took the clearlake way which is lots of twenty to thirty miles an hour windy hills. It was a good one hundred degrees outside and as soon as we hit the hills the temperature gauge started to rise not all the way to red, but to much for my comfort. If I kept the heater on full blast or stayed at 80 to 90 it would stay fairly cool. But it did seem to overheat more when I had it on cruise control or had the ac on and of I went above 90 it would do it again we stopped half way home drained the radiator and filled it back up with Lucas super coolant and it stopped doing it as bad. Now that I am home in cooler weather the gauge does not raise as high ans when it does its only in traffic when my ac is on. I have not changed the water pump since I have had it. The thermostat is brand new and my cooling fan comes on then shuts off I am wondering if it is the water pump or if it could be something with the air conditioner or a leak. I also noticed when we drained the radiator and refilled it was low and I burnt a quart of oil on a six hour trip.