I have had my LS1 for 2 years now, but recently my car has begun backfiring since I moved to TX from UT. The car only backfires between 3000 to 4500 RPMs. Also when I decelerate it sounds choppy. I have Kooks headers and true duel exhaust, but it never backfired or had so much back pressure that it popped. I did a complete tune up, new wires, plugs, oil filter, oil, fuel filter ect. I have had a O2 sensor high voltage error code, but it went away, and had appeared before, but went away a day after it appeared. Anybody have any ideas?