The rear striker is too high or low.

Inspect for witness marks on the locking cam of the rear latch. Adjust the rear striker.

The center roller track is misadjusted.

Adjust the center roller track so that the roller rides in the center of the track.

The locators are too high or low.

Close the sliding door and observe the feature line. Adjust the lower locator if the feature line goes up or the down.

The door sticks to the weatherstrip

Run a finger over the weatherstrip. Replace the weatherstrip if the weatherstrip drags.

The rear striker is too far inboard.

Adjust the rear striker.

The front of the door is too high in relation to the opening.

Inspect for witness marks on the inside pockets of the locator holes. Adjustment of the lower roller bracket UP lowers the door.

The door header clearance is too small.

Remove the roof rail weatherstrip and close the door. If efforts improve, reform the header for more clearance.

The upper roller is out of adjustment.

Reform the upper roller bracket in order to eliminate vertical loading on the roller.

The upper roller bearing fails.

Replace the upper roller bracket.

Dirt is in the track.

Clean and lubricate the track.