94 Corvette PCM Mystery

[Red Rocket]

For the past year, my 396 LT1 runs real strong on the dyno. When I get to the track, the car is running 5-6MPH slower and 3-4 tenths higher than previous times at the track. The dyno supports the higher HP and better ET's. Comparing my times with other Corvettes at the track, there is no doubt I'm down 60-70 HP at the track which is not showing up on the dyno. The issue started when my speedo was jumping all over the place even when not moving. Shop thought it was the speed sensor but recommended replacing the computer. Replaced the computer and still have the same problem. ASR service light came on and we ended up disconnecting the ASR since it will impact timing and the throttle. Car still having the same problem at the track. Any thoughts on what can happen at the track that will not show up on the dyno from a PCM standpoint. The problems all started with the supposed initial computer problems.

[simple green]

Just a guess, but maybe you're getting "knock retard" from hard shifting and not when dyno tuning.