Check the transmsission fluid level May be time for a rebuild
Is this an automatic transmission?
Probably the shift linkage in that model.
Just right into the test stick , check level with engine running, apply gear shift back and fore then parking before checking level
If the transmission won't shift out of first gear on a 1992 Buick Roadmaster, it could indicate the transmission gears are seized. It can also indicate a low fluid level.
clean out or replace the throttle body spacer...
Check side of transmission
Worn trans or diff parts. If it gets worse, have it looked at.
If it's an automatic transmission the linkage needs to be adjusted. On a manual transmission when it pops out of gear it means there may be a bad synchronize for that gear a mechanic will need to repair. Once in a while a manual transmission will start doing this if it is low on gear oil.
Regal Beloit Corporation, manufacturer of Generators, Electrical Motors, Gear Drives and supporting products in the Power Transmission industry is headquartered in Beloit, WI.
Check your transmission.
Its gear oil
My 1998 Nissan sentra wony shift into high gear