I have a 2002 GMC Sierra 2500HD, 6.0 with Automatic. I changed the oil, backed the truck out of the garage, put it in park, shut the garage doors, got back in truck. Pushed brake pedal, Shift lever moved down, but felt like it went way to easy. It doesn't feel like any linkage is moving. Don't have any action, forward or backward, nothing. Any ideas? Thank you