Align the shift indicator orreplace it. Your problem is strictly column mechanical.
My Mom had the same problem with her truck.. It is due to a recalled part that is on the brake master cylinder
Sounds like a torque converter lock up solenoid.
its going to be some were on the tranny a small metal rode is going to be connected to the park/shift solenoid and that metal rode runs throw and connects to your shift handle inside the car/truck
The cable between the shift lever and the transmission may be bad.
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Best source is GM shop manual, for your year truck, which is usually available off eBay There are also manuals available for download at various sites for a price
there is a small string ,and spring connecting the gear selector needle, and the shift collar on the steering column. that is what has to be replaced. you should be able to remove parts of the dash to get to it. It usually isn't a big job.
footbrake deactivation switch
Shift cable needs to be adjusted.
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.
Check to see if the stop lights are working - shift interlock and brake lights are on the same circuit Check fuses