1998 Buick Regal stalls

Could be a couple of things. First remiove the thermastat with the engine cool and back flush out the system. The radiator or heater core may be getting clogged up. Replace the thermastat that could be going bad. There is one thing to do before you do all that is check between the radiator and the a/c condensor core to see if there is anything that would cut back on air flow. The reason I am saying it is that I had a 1995 buick regal and it was overheating. Changed thermastat and flushed out system. The car had been sitting for some time under some pine trees and the pine needles got between the rad and ac/ condensor cutting off air circulation to the radiator. I could not see it until I pulled out the radiator.