Yes you need to make sure you never park the truck without using the parking brake. What happens is if you put the truck in park and then let your foot off the brake the truck will roll forward or backwards and the entire weight of the truck will be resting on the little parking pawl inside the transmission. If you are on any type of incline push your truck up the hill somehow maybe with another car or truck then see if it can be taken out of park. The procedure for parking should go as follows to prevent this from ever happeing again.
1.) Stop Truck with brake and keep foot on brake
2.) Shift truck to neutral
3.) Apply Parking brake all the way then remove foot from brake pedal so the truck is being held in place by the parking brake only
4.) Put truck into Park and shut off.
If you do it this way and just make it a habit you should not have the problem ever again assuming that this was the problem to begin with.
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