That temp light worries me. Don't have my books in front of me but many cars have two temp sending units. One for the gauge and one that feeds the computer which controls the light. I have a feeling your thermostat isn't opening and your engine is overheating and that is what is causing the engine to start running rough. The gauge sensor might be close or on the radiator and the computer sensor might actually be in mounted into the water jacket. Your light is telling you there is no coolant flow through the engine causing it to overheat while the gauge sensor is telling you the radiator water is warming up just because of the radiant heat from the engine. Check to see if you see water flowing past the radiator cap to determine if the thermostat is opening.