I have noticed like hcvone said, that you will notice a difference after about 100 miles with a relearn. After I had my headers installed, it seemed like it took about 300 miles before the PCM was happy.
-Speed
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2001 QuickSilver Z06
Lowered,178 thermostat w/ fan controller, Ripper, !CAGS, B+B PRT w/ Speedway tips, TRIC one-piece with CF Cobra, GMS MAF, and TPIS long tubes
AOL IM: Speedshift