J-mod and tuner

optionizerSS

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Last summer I did the j-mod on my step-sons 1999 GT. Worked great. He recently bought a tuner mainly because he has an off road x pipe and his CEL is on and it was running rich. He bought an older tuner to turn the rear O2 sensors off. After that the car started shifting differently. No tune, just adjusted his speedometer for the gear swap (3.27 to 3.73's) and the O2 sensors. He reduced line pressure by 5% using the tuner and it was a little better but not sure that is the best thing to do.
Anyone else have this issue and how did you fix it?
 

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