Hello Scotty!
I own a 1996 Buick Park Avenue with GM 4T60-E transmission.
The car shifts from 1st to 2nd just fine... and then stays on 2nd gear until 50 mph.
After about 50 mph, the car shifts to 3rd, then IMMEDIATELY shifts to 4th.
So it seems i never drive with the 3rd gear. Which leaves me to drive with 2nd gear for most town (40 mph) areas.
Do i need to replace the transmission? rebuild it? Is there a computer system that i need to reset?