68 c10 tailgate question....

[WinDancer]

I am just finishing up my years-long build on my 68 C10 SW Stepper.
When we painted my truck [John Deere Blitz black] we took the bed completely off the truck and removed every nut, bolt, panel and screw.
After paint we put everything back together and I decided to change the closers over to the seat belt latches.
Got them ready to go on this last weekend and used double sided carpet tape on the backs to hold them in alignment.
Went out to the truck and found that the tailgate did not fit properly. I have had the truck many years and the tailgate always fit just fine.
The tops of the bed rails are too far apart. There is also some slop side to side, maybe a half inch or so.
The only parts that were changed are the bottom pivot bolts/bearings and new wood in the bed.
When I found myself with a strap tie-down in my hands I closed the truck shop door and came inside.

Anyone ever have this problem? What do I do to correct the fit? Hands-on experience only, please

Huge thanks for any help!
Dave