gear change on 98 Camaro maxed out pulse per distance and trans rev/mile still off

[COAL TRICKLE]

Working on a 1998 Chevy Camaro that the rear axle has been changed. The owner of the is not sure what gear ratio it is but the speedometer was 40 mph fast and the car shifted very late and had a very hard 1-2 shift. The tires are 225/55R16 so I did some quick math using 25.7 for the tire diameter so for 4.10 a multiplier of 6.268- 3.73 6.89 - 3.42 7.515 - 3.08 8.344 - and 2.73 would be 9.414. So, I started with the 4.10s and threw 6.27 in the tire/gear wizard and it went the right way now i was 30 mph off. The problem is now I'm very close to maxing out VSS pulse/distance and Trans Rev/mile, but I know that's the way I have to go. The lowest value I could put in G/T wizard is 6 so I tried that, and it maxed out VSS pulse/distance but not trans rev/mile. I drove it now was 20 mph off still shifted late and had a hard 1-2 shift. I maxed out trans rev/mile and the shift was a little better but no change to speedometer. Next, I changed the tone wheel count from 40 to 30 just because I'm runing out of things to adjust. This made a big difference in the shift scheduling, now the shifts felt pretty good, 1-2 still a little firm and the speedo still off 20 MPH. I adjusted the shift pressure and for 1-2 and increased the shift time for 1-2. Now it shifts really nice but I'm still 20 MPH off on the speedometer with nothing left to adjust. Does anyone know of a fix for this? Can I flash the IC or PCM through AC Delco or is there a later PCM I could use with more adjustment?

[COAL TRICKLE]

Just ordered Dakota Digital Universal Speedometer and Tachometer Interface which will allow me to re-calibrate an electronic speed signal. Still up for any other suggestions if anyone has any?

[RDF1]

Have you tried to spin the pinion and see how many turns it takes for the tire to make one revolution?

[COAL TRICKLE]

Yes about 4 and a half so guessing 4.56s but doesn't matter that would be 5.6 multiplier and can only go down to 6. Never ran into this before but if anyone else dose Dakota Digital Universal Speedometer and Tachometer Interface worked for me.