Stepside bed - one side leans

[Hair]

1971 GMC short stepside - New wood installed, bed all back together, everything straight, and square, and level, all bolted down. Only problem is, when I put on the tailgate the passenger side is leaning outward at the top, so I got to push in on it hard to bring it in to enable the tailgate latches to fit into one another so the tail gate can shut. Surely others have had this issue before... my question is how do you fix it? I was thinking to hook a come-along to it and try to bend it inward, but thought I'd ask to see if there's a better way, or if that would even work. Note: It also had this issue before I ever took it loose and put the wood in it, I thought once I put the wood in and squared up everything it might go away,,, nope. That rear fender had to have a lot of sheet metal patching done, I 'm thinking maybe it could be twisted and causing the bedside to lean out now, but that's just a guess. It's out about 1/2", at the top. Any advice appreciated.