Q: Truck won't go into park

There can be a few reasons why your shifter would be jamming up or sticking. The gear selector is apart of the shift linkage controlling what gear you want to enter. Over time, mechanical parts wear naturally and the linkage can loosen up or bind in some situations. If any section of the linkage has begun to fail, binding can occur. Also the actual mechanical components of the transmission could be failing. The parking cable used to keep the vehicle in park and unable to roll until the driver is ready to engage a drive gear. If damaged the parking cable could cause such an issue as difficulty entering and exiting park. A proper inspection of your linkages and transmission should be carried out by a qualified technician like those here at YourMechanic.