1996 Z28, I haven't had the car long, runs good no issues over than the trans shifts really hard 1-2 and 2-3 shifts normal after that. It doesn't matter throttle position. I'm wondering if someone has reprogramed the computer to change the shifts. I wouldn't mind the hard shifts at WOT put the neck jerking shift when normal driving is a little much. Does anyone have any ideas?

Thanks in advance.

 

look around for a performance unit/chip added under the hood. are you seeing a service engine light? could be trans is not happy. valve body could have a sticky valve or a failing solenoid.

 

Not getting any service engine litght. I don't remember seeing anything that doesn't look factory but I will give it another look.

 

Hopefully Gary will read this. I would love to know if you can use a basic scan tool to verify an edit date on the PCM programming. I would hope that if the PCM was reprogrammed either the mail order tuner or PO would have left some information on what was done and by who. I am not sure PCM can have an effect on shift harshness, I believe it controls when the trans shifts but harness is a factor of hydraulics.

Common upgrade to the 4l60's is a tuffer accumulator springs. This will cause a harsher shift while protecting the clutches from wear. The Vett accumulator springs are slightly stronger but aftermarket ones can take it to a whole new level. There are still shift kits that will raise line pressure. A shift kit with an aftermarket accumulator will hurt your neck. A transmission should be upgraded to handle that. Hard shift save clutches but they can break everything else.