Papicamper is correct. The big Black plastic cover is in effect your lube plate. Do not use the white lube plate. Also there are times when you have some stress on your hitch for whatever reason and your your hitch will not unlock when trying to unhook from the 5vr. Set your park while hitched and use chocks on the tailor then put the tranny in neutral. This procedure will sometimes relieve the stress and allow you to unlock the hitch.
BTW, The new 20,000lb Reese hitch is much improved over the previous model. Tolerances are very close thus making the new model very quite and eliminating that slamming sound that some hitches have. really like our new Reese.