Ok, so I just got my car back earlier today from Speed Inc. I previously had headers y-pipe, and catback installed. I had Speed Inc. install my VIG 3800, tranny cooler, and do a basic tune to get rid of my code from no O2 sensor, etc... New converter works great, however as i was driving today, i was on a side street, made a normal slow moving turn at a stop sign, and the engine sputtered. Almost sounded like it was mis-firing. Then after that the car was running lean the entire time....drove it for like 10 minutes, got on it a few times, still lean, and now the check engine light is back on!!! Engine vibrates more than normal now. Gonna have it looked at tmw i think. Any ideas whats wrong??? Ran great for about an hour, now this!

 

I don't think this is a problem that could be diagnosed in the automatic trans section. I'd try the PCM Diagnostics and Tuning section or the Fueling and Injection section.