Over heating car

I have a 98 Buick Century, with about 250k miles on it. Recently when I first start the car and drive a few miles the temperature gauge keeps rising until it is in the red zone and a warning light comes on. When I pull of to the side of the road after a bit it begins to slowly drop and I can begin to drive again. The gauge will then normally stay a bit above halfway for the remainder of the trip, the gauge has sometimes done a bit of jumping around between 3/4 and half sometimes though. The only work that I have had done on it recently is to have some work done on the ac system. Just wondering if anyone could help me find out what is going on.

First thing is to check the level of coolant to make sure it is ok. Then it could be a sticky thermostat, or heaven forbid a head gasket which is not something you want to do.

My vote is on a sticky thermostat. And, if has been a few years since the cooling system was serviced, I’d do a complete coolant drain-n-fill with a rinsing of the radiator and new thermostat and radiator cap. Also, it would be an ideal time to inspect heater and radiator hoses, replacing any that look suspect.