CONTINUED:
Now onto reworking the main "body" of the unit. Again, this is what helps the actuator rods to return to "neutral," releasing pressure from the latches themselves. If your latches work ok now, but it's still hard to keep the tailgate shut, the rods are probably not returning to the resting place.
If you've reinstalled everything to test the new/reworked latches, uninstall everything again. Once the main body is free from the liftgate shell (by removing the (3) bolts that held it in), you now need to get it out and onto a workbench. This can be done (2) ways, and chances are good that the easy way won't be an option:
1) The easy way: The body comes out after the actuator rods are removed. The actuator rods are connected to the main body via threaded ends that connect to little "nubs" that are clipped onto the main body (you'll see what i'm talking about) - they're probably under a coating of rust, which will prohibit you from doing this the easy way. Technically, the actuator rods are adjusted by screwing them either in or out to achieve the perfect amount of pressure, but most of ours are covered in rust and cannot be done this way.
2) The hard way: You need to remove this 6' wide part through one of the 1'x1' holes. A lot of back-n-forth, over/under/around the wiper motor, etc. This is a PITA but i had to do it. You could remove the wiper motor, which will help, but it's just something else to reinstall.
Once it's out, you should be able to remove the actuator rods which will allow you to reinstall them after you put the body back into the tailgate. While it's out, clean it up (brake parts cleaner(?)). A good wire brushing helped too where obvious rust had set in, hindering the part that the actuator rods from returning to neutral. If it's cleaned up and operating well, (play with the center pivoting part to see if the (very small) spring is actually doing it's job), lube it up and reinstall it. Mine wasn't, so I tried adding a spring to it, but the body was still binding and the springs weren't strong enough so i decided to wait and replace all of the guts. If yours is working, lube it up and reinstall. (i opted to replace this part, as the amount of rust was so great that i couldn't get it working well enough - but that was on another trip into the liftgate).
Remember, when putting it all back together, remember that proper alignment and reinstallation of the short actuator rods (to the glass latch, the lock cylinder, power lock actuator, etc) is very important. When i put it back together, i didn't align something quite right and the manual hatch lock (the one you see go up and down when pressing lock/unlock) binds, adding undue stress to the power actuator.
If you plan to keep your X for a while, i would advise a complete northeastern overhaul (latches, rods, body, lock cylinder - approx. $100 from a (southern/western) junkyard. Take it apart once, see what the problem areas are, fix what you can, and then find the rest through midwest mustang or someone here that's willing to part out a tailgate. My wife loves me for it.
PM me if you've got questions. I assure you that once you "see" these parts i've described, you'll be fine