I have the same problem on my 98, honest to god, I get out of the car, put my shoulder on the rear and rock the car back and forth as if I were tryin to push someone stuck in the snow or mud. Works everytime.
The cable between the shift lever and the transmission may be bad.
Shift Cable
Align the shift indicator orreplace it. Your problem is strictly column mechanical.
Answeryou must step on the brake pedaland if that fails.there is an emerg. release on the left side of shift console.lift lid. slide bar, shift.
footbrake deactivation switch
Check to see if the stop lights are working - same circuit for shift interlock and stop lights - check fuse Try turning key to 1st (unlock) position Shift to Neutral Start vehicle and then shift to "Drive"
I don't know for sure but on some fords if the fuse for the brake lights is burnt out it will not shift from park. On fords if you turn key part way to on position then shift to neutral and start engine. Do not use park till you get fuse replaced. Mine blew because of bad trailer light harness. Sorry if this does not work on chevy.
vacuum leak?
Shift linkage out of adjustment?
My 1999 Chevy Malibu does the same thing. Make sure the gear shift selector is actually clicked all the way into park (push or pull it until the button clicks). The key cannot be turned all the way to the off position (and removed) until the car is in park.
linkage to transmission poped out!
You did not have to apply the brake on a 91 model to shift it. There's nothing wrong.