on your tailgate hinge,look for a little hole to squirt oil in, maybe take it apart and clean or ream the hinge hole, Welcome to the hood,learn a lot here.
I'm one of those guys thats still spending money on my jeep and still saying "I got a helluva deal. 91 yj,2.5l,5 speed bought it for 500 dollars,got a total of 2500 dollars invested in it,has 127000 miles" I are happy camper"
attached is photo the way I bought it.