Looking for stock transmission/ speedometer settings for 1998 Camaro V6

I have a customer who bought a 1998 camaro convertible v6. I've done several tunes for their family. this is Mom's new purchase and she loves it. the speedometer was reading 75 MPH at an actual 50 MPH. 3.08 gear matches the RPO code. Vin in computer is the same as Vin on car, (I thought that someone might have swapped ECU. By maxing out the VSS pulses per mile at 131,070 I can get the speedometer within 5 MPH, (56 on dash, 60 on GPS) and though the shift points re now much more sporty, the car never sees fourth gear. I can of course adjust the shift speeds but I would love to get a compare file.