Shifter Trouble

Since yesterday my old man's 1995 Hardbody (Auto. Trans.) is being very stubborn about shifting out of park. At times, it seems like it is locked in position and we can't drop it into reverse for nothing. Any ideas on what could be causing this to happen?
Also, about a week ago he had to have a little round plastic piece on the brake pedal replaced because the brake lights were stuck ON. Don't know if there is any link between the two..........

maybe the linkage cabel i had a sonoma that did this a few yrs ago

Soaked the maze of rods and connectors with WD-40 and it magically started shifting again! Apparently had too much old grease and road grime built up on them.............

if its an automatic, you should first check to see if you have enough transmission fluid. thats what my problem was