Currently I need to slam my upper tailgate closed in order for the latches on both side to catch. It seems like the left side latch is just a little bit too far back, but it does not look like there is any means to adjust it.
The catch can be adjusted loosening the two posidrive screws on the striker (sticky out bit on the body).It is better not to totally remove the screws as it is made up if (I remember right) 3 pieces. Be careful to use the right size drive as it easy to round off the screw indent (I have been there). It may be useful to use a flat bladed screwdriver to maintain the correct distance as you screw it up as the spacer tends to move, this will be obvious when you do it.
If this does not work check to see if the spacer is enough as the bulbous part of the striker may be clashing on the tailgate!
I have to do the same thing on mine. I actually slam it shut by placing my hands on the outside corners. Seems to work well enough.
Then I decided to take it apart to see what makes it tick! :bawling: Do NOT attempt this. 4 hours later I was still trying to get it back together right! :complain: BUT after lubing all parts with WD40 and probably doing the fix noted above :lol: by default it works well enough that I do not have to rattle the body to close the hatch anymore!!
So I would do the above AND spray liberal amounts of WD40 into the working parts.