I have a 1996 Pontiac Firebird Formula TA with a 5.7L Automatic Transmission. I

What is your question?

I was told later that this 3.73 posi-track 3rd member has 7 splines and my original 3.23 had 11 splines. It has obviously affected the speedometer. Has that also affected the transmission? My transmission is a 4L60-E with a street/strip torque convertor. I really like the lower to mid range increased acceleration, but I sure do miss the higher speed without the overdrive. Any suggestions? Other than that everything mechanical on the car works great and no check engine lights. I just had it inspected yesterday.

What makes this problem better or worse?

N/A

How long has your 1996 Pontiac Firebird had this problem?

Since the 3.73 gear was installed.