I would have your fuel pressure checked out, check your fuel filter, it is possible you got bad gas but not likely the problem, My 93 grand Prix w/3.1L used to run really rough when it was wet outside till the car dried itself out, I figured out one of my wires needed to be replaced the rubber was worn. its someplace to start. You could have a fouled plug which would make the car run on one less cylinder.. It wouldnt hurt to pull a plug and see how it looks.
-Jimmy