If the transmission is electronically controled, it will shift gears based upon rpms, not mph.
Since you have a 95 transmission, it is a AODE transmission as San~Man said. Not a 4r70w automatic. The only thing the speedogear will do is help to give a more correct speedo reading for the gear change. However, a speedo gear is but only so accurate.
If you have the stock vavle body and no aftermarket shift kits, then there is a good chance your transmission will not shift accurately. I say this because the stock computer programing and shifts are based on the stock rear end gears and the time it takes to clear certain rpms levels with those gears. Wether it be wide open throttle or partial throttle shifts. The computer sends a signal at a certain rpms to the transmission to begin a gear shift. At this point, certain electronical shift solenoids begin their work by feeding line pressure to certain pistons and clutch accessories in the transmission. Now, the idea is to get the transmission to shift by a certain target rpm which is typically red-line if you are full power on(WOT). Typically speaking, it takes the computer about 1 second to complete a shift from the time it begins the shift to the time the engagement of the following gear is complete. If you want the car to shift at lets say 6k rpms at WOT, the computer needs to begin the shift process about 1 second of WOT rpms before 6k rpms. Which with the stock rear end gears is about 1,000rpms before the target shift rpms. When you go to a steeper rear diff. gear, the motor will pass through each 1,000 rpm incriments faster than before due to the difference in gearing. The computer with stock programming however, is unaware of the gear change and therefore will have shift patern programming for the stock rear end gears. So, when at WOT with steeper gears than stock w/ stock ECU programming, the computer will still begin its shift about 1k rpms before the target shift rpms when it needs to start the shift process a bit sooner. Since it doesnt start sooner, there is a very good chance the shift will come later than needed and the motor may very well hit the rev-limiter before completeing the shift. For this very reason, you need to get the ECU flashed or a sport chip when doing a gear change in an AODE car.
I hope that helps out. Basically put, you need a chip or ECU flash when doing a gear change.
