Welcome! I'm Ron Z! Make sure to use Reply if needed! And PLEASE remember to RATE my answer at the end!
When the shifter will not release from Park, check the rear brake lights and see if they are working when the brake pedal is depressed.
if the light are not working, the problem will be the Stop Lamp Switch located at the top of the brake pedal arm. Most commonly, the internal plunger of the switch is faulty, so unfortunately, "cleaning" the connections will usually not solve the problem. Inspect the electrical connector for any loose or broken wires. Inspect the switch mounting points and make sure there are no loose or missing parts. If the visual inspection checks ok, replacing the switch will solve the problem. This is actually the more common problem on these vehicles.
If the brake lights are working, and still will not shift from Park, the problem will be in the Shift Interlock System. More commonly, this is a problem with the Shift Interlock Solenoid. Again, usually an internal failure, so "cleaning" is not usually a cure. The solenoid is mounted to the side of the Shifter Assembly. Inspect the electrical connector and inspect the Shifter Assembly for any problems that may keep the solenoid from engaging. If the visual inspection checks ok, replace the Solenoid.
*** PLEASE REMEMBER TO LEAVE A RATING FOR MY ANSWER! RATING THE ANSWER IS AN IMPORTANT PART OF THE Q&A PROCESS! ***