1997 Pontiac Firebird Multiple Random Misfires

I thin it is the gas, I would run the tank out and get gas at a station that pumps a lot of gas.

Gasoline will deteriorate after 30 days.

You can remove fuel filter, pour contents int clear glass, it you see two seperate liquids, then you have water in there.

I know this is an old question but ....
It could be several things,
checking the gas is a good first step if that does not work
it could be with the evap system. check and or replace the Canister Purge Solenoid(found in engine compartment), and Canister Purge Valve(found next to the evap canister by removing the dust cover on the driver side quarter panel directly above the rear driver side tire). also check and replace the evap canister located near the same place as the purge valve but closer to the filler neck. If after all that you clear codes and still have a problem it is probably time to spend some really money (sorry to say) and get a new catalytic converter which on these car are really over price but it will fix the problem. By the way if shopping online the evap system parts can usually be found under the emissions category of most auto parts stores.