What is causing my check engine light to flash? on 2004 Chevrolet Impala

On a very rainy day, I got some gas from the Shell and 15 miles later, my check engine light starts flashing and my car starts shaking as I accelerate.. Pulled over to the side of the road and my exhaust smells like I just fired off some fireworks.. Exhaust from the tailpipe is colorless... Took it to auto zone and I get the code for multiple misfires, system too lean, torque convertor sensor stuck on "On",and something about my fuel gauge.. Please give some idea of what wrong so I don't get highway robbed by a mechanic lol..

tell us what the code was and check to see if your gas cap is on right