Was changing ATF on my daily driver and I think the automatic transmission may be now in limp mode or something. Car is now in 1st gear and won't shift up. At first, the gears were shifting after the ATF change, then when I had to drive the car a little harder to pass someone, the car went and got stuck in 1st. I didn't fully tighten the tranny pan so maybe that caused this? I also changed transmission filter.

This is a 1988 Buick Park Ave w 134k mi.

I disconnected battery for 6 hrs and steped on brake in hope of resetting tranny ecu. Still stuck in 1st. Any ideas??