I have the same hitch and the same problem. I picked up some slide out gear lube from general rv, it did the trick for the most part, I sprayed the rails but that was last year. I didn't do it this time and it cost me. I normally don't have to slide it, the fivers nose has always cleared but I should have listened to the words of caution I have been giving others. If the truck or trailer wheels find a hole while you are jack-knifing the trailer it can hit and I was right, I caught it in time and a minor scratch was the result.
Anyway, whenever I can't get the hitch to slide I drop the landing gear and take some of the pin weight off, it slides very easily once you do that.