Truck problem: dificult to shift from Park into Reverse

Quick check of shift solenoid is to press brake and see if you hear/feel a click in gear shifter, if so the shift solenoid just released. If not, the solenoid is hanging up. Disconnect the cable at trans while in park and see if hard to move when cold, if so cable is sticky when cold, but warms up and works when hot. Either way I think the cable will need replaced...solenoid is part of cable on most vehicles, so I would plan on a cable.