I have a 99 black Firebird Formula A4 w/71k miles that is stock w/ a lid. I noticed while launching my car, after sitting in heavy traffic, my trans slipped? I spun slightly all the way to the top of 1st gear when it hit the rev limiter. (it does this sometimes, especially after spinning).

I was looking at the tach when it shifted and it dropped to only 5500 or so then kinda slowly dropped more. Can I use my autotap to test for trans slippage? Is my trans going out? Would installing a shiftkit or using a HPP to increase firmness extend the life of my trans?

 

You should be able to look at the TCC Slip Speed parameter. Despite its name it's more than just the difference between engine speed and input shaft speed. It's probably only useful to look at it when the converter is supposed to be locked unless you have lots of historical data to compare to. With the TCC locked, speeds over and above 30-40 RPM are typically due to internal component failure. (The P1870 DTC uses this parameter for exactly this sort of thing.)