I have an LT1 in my K5 and just finished swapping it in but my combo of 33 inch tires and 3:08 gear ratio = my truck going no where and almost stalling every stop light. I'm swapping in a 4:10 or 4:56 ratio but how important is it to program my PCM after I do this swap?

 

The biggest thing is that your speedometer is going to be off if you dont reprogram it. For a manual I dont think anything else is effected. There may be other issues with an automatic such as shift points.

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Greg
95 Z28 conv M6
Georgia F-Body Association

Stage 1 heads, 1.6rr, Meziere WP
lt4 hot cam,lt4 timing chain kit,52mm TB,
Hooker Headers, Pro 5 shifter,3.73s,
NX 150 progressive,
Self-tuned via Tunercat

 

Yeah, that's my issue, is my transmission 4L60E going to be alright if I change the ratio in the rear end?

 

Your A4 WOT shift points will be off. If Im not mistaken the car will shift sooner than youd like it too.

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96 black Z28 A4
GTP heads, GTP cam, bolt ons...
Mattucci Motorsports WNYFA FLFB
So far...12.7@108...need more practice...
The Z