Definitely lube the hitch head bolts, we had some trouble with ours until he lubed it and worked it loose. BUT, if that thing is at an angle, it is going to be hard to get off the l-bracket. And depending on the angle, raising the tongue jack can sometimes make it worse. Like others, I use a hammer, though I found a big rubber mallet did the trick just fine, without the noise.
Current TV:'14 F350 Lariat CrewCab, 4x4 Short Bed SRW Diesel w/ Pullrite 2700 (16K)
Current Fiver: '15 Puma 295BHSS Anniversary Edition
Past TV: '13 F150 HD Payload SCrew EB, '08 Tundra CrewMax 5.7L, '02 'Burb 5.3L, '97 Dakota 3.9L
Past Trailers: '09 Wildwood LE 27RB, '02 Palomino Yearling RL, '87 Jayco 1006dlx