Ok so heres the problem. My car has only long tube headers, no cats, 3" y-pipe into a hooker 3" cat back, and a k&n air filter. When i first go the car, in october I believe, I changed the o2 sensors. The car ran fine with them until about a month and a half ago, car started running really bad, hesitating backfiring, ect. Same thing it was doing when i got it, so i changed the o2s again. Car ran fine for about a week.So I ran 2 tanks of gas and seafoam through it and cleaned the o2 sensors today. She ran pretty good, no signs of what it was doing, although didn't feel as fast. About 20 minutes later it started acting up again. The only thing i can think of is that its running too rich/lean and keeps fouling out, I just don't know why it fouled the new ones out in a month when the other ones lasted 8 months. I had a basic tune done when i got my 9" put in and the only engine light i had on was for the skip shift, which had a eliminator pugged in. I scanned it at the shop the other day and it had about 9 codes, mostly protaining to the o2's being fouled. Does it need to be tuned? Any suggestions would be nice

Thanks
Chris