Lumina problems

I have a 93 Chevy lumina (Eruo) with a 3.1L and it is runnig rough. It sputters it chugs when you step on the gas and the exhaust has a rattle to it. Now i fill this car up one day at a cheap Ma an Pa type station then the car ran hot and started to run rough now its really bad i changed the thermostat and it doesnt run hot anymore but still has all the other problems. Do you have any Idea

Check to see if you have a miss fire. check plug wires to see if thy have enuf lube of if their dryed out. You might want to check the exaust to see if it pushing or sucking air (converter)dougie3980