locked shifter stuck in park

[cdjacks1]

I have a 2008 silverado that is staying locked in park instead of shifting in to gear. I have tried shutting ignition on and off, releasing and depressing brake pedal and putting ebrake on.
Frees up after numerous tries but seems to be getting worse.

Any suggestions thanks

[way2old]

Check the brake light switch and the connection to it. if the ECM does not recognicze the brake is on, it will not allow the shifter to move.

[violadav]

My car also suffers the problem in its transmission as I am suffering a pretty noticeable fall in pic-up when in third gear. I have contacted my mechanic and he says there is a spare in transmission assembly needed to be changed which is not available locally. Can you suggest me some good option?