1991 Cadillac Brougham Transmission/shifting gears

You may have an electrical issue, or you may have a mechanical one. First thing you can do is check the fluid. At full operating temp, and at idle in park, check the level. If that's ok, look at the quality. Good fluid is red or pink and smells sweet. If its the color of coffee or tea thens its time to go. Poor fluid will also smell burnt. If you've never done it, get the fluid and filter serviced in the transmission. After all that if theres still a problem youll need to get to a trans shop to get the mainline pressure tested and the shift solenoids checked if it has them. This transmission was built at a time when there were still some transmissions that weren't all electronic, so thatll have to be determined as well to know if you've got an electrical problem