I have done the tpi swap in my 91' and it orginally had 2.73 gears and I installed a set of 3.42's. I have not changed my drive and driven gears yet, but am still driving the car. Will this incorrect vss reading to the ecm change the way it delivers fuel/air ect...? It's still reading the 2.73 gear ratio with the drive and driven gears I still have in my 700r4, but is turning much faster with the new gear set...any issues?

 

I've been driving my 86 IROC for 2 months now with a 3.08 (BW 9 bolt) rear end in it after my 3.42 (10 bolt) gave up. It's TPI as well. So far it's running great. Last mpg check was 20 driving it back and forth to work in mixed stop and go and highway driving. I believe our set ups might be different though. I have a cable running from the transmission to the speedometer and VSS in the dash. You should have a wire running from a sensor in your transmission up to your dash. That may not make a difference though.
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I've been driving my 86 IROC for 2 months now with a 3.08 (BW 9 bolt) rear end in it after my 3.42 (10 bolt) gave up. It's TPI as well. So far it's running great. Last mpg check was 20 driving it back and forth to work in mixed stop and go and highway driving. I believe our set ups might be different though. I have a cable running from the transmission to the speedometer and VSS in the dash. You should have a wire running from a sensor in your transmission up to your dash. That may not make a difference though.

 

It will change when the torque converter kicks in around 35 MPH as seen by the computer. Other than that, the computer just needs to see a speed increase.