1992 Ford Mustang Sticking after reverse light switch repai

Transmission problem
1992 Ford Mustang Two Wheel Drive Manual 192000 miles

I have a 92 Mustang GT. Backup lights were stuck on, so I bought a new reverse light switch and had it replaced. The old reverse switch was slightly scuffed as if it was being ground down. 5th gear was already going bad beforehand. The first day it acted fine. Now, the backup lights are stuck on and the car is stuck in what seems to be either 5th or reverse. You can shift into all gears except you have to force it into reverse. When in 1st through 4th it usually responds as if in reverse. When in neutral it seems to act as if in fifth.