Reddit reviews Drawer Slide, Full Extension, 36 in., Heavy Duty, 500 lb. Capacity, Zinc

That is an interesting idea for hiding a TV, I've never seen anything like it. That being said, it looks like the doors are running on a normal drawer slide. So I would guess that one of two things are happening right now.

First is that drawer slides are not meant for this application. Any lateral force pulling the door away from the wall or uneven load, could throw the slides off balance, cause twisting and cause extra friction. I would see if there is a track at the top or bottom or a retaining rail keeping the door from straying from the intended path, and putting extra pressure on the slides. If there isn't one, I would consider adding a retaining rail of some sort to prevent that from happening.

My second idea is that the installer might have used standard drawer slides that aren't meant to hold that much weight. So the slides have worn out over time and they don't work like they should. They make heavy duty ones that can hold more, and a switch to those might work out. Depending on the weight of each door, you could look at something like these:
220lb: http://www.ovisonline.com/30-Drawer-Slides-220-lb-Heavy-Duty-Full-Extension-P1693.aspx
500lb: https://www.amazon.com/Drawer-Slide-Extension-Heavy-Capacity/dp/B0009OBPH4
The weight is per pair of slides, you only showed 1 slide for the door in the picture, but I'm assuming there's a second one at the top. If not adding one to the top might also help. Remove and weigh the doors to determine the slides you need, bigger is going to be better here since this is a non-standard application. Also make sure to measure for the length you'll need on the new slides.

I used these for the locking slides and these for the non locking. Figured I just needed one side to lock. They are pricey but they are heavy duty for sure.

My wife and I used to do a lot of overlanding in my 2001 forester in much the same way that you describe. We had a similar setup to your third inspiration picture, although we had quite a bit less space under the bed than that.

I built a wooden platform out of plywood that was basically exactly the same height as the rear wheel wells (the forester has a flat spot on top of the rear wheel wells). I cobbled together a wooden frame that just rested in the back of car, it wasn't actually secured to anything because I built it into the car so there was nowhere for it to go. That left me about 10 inches below the platform for storage. I had just about 3 feet of space between the rear door and the back seats to work with so I installed 2 sets of heavy duty drawer slides and built some shelves out of cheap plywood. I added a few dividers and a mount for a camping stove on one side, and left the other one completely free of dividers.

This basically gave me 7,000 cubic inches of storage on each side, so one was usually food, cooking supplies, and utensils and whatnot and the other side was usually camping gear like clothes, furniture, binoculars, climbing gear, axe, lantern/flashlights, and toilet paper.

I can't really take any pictures because I tore it apart after our second kid and needed to haul kids in both of our cars.

EDIT: You might have pretty good luck posing this question over in /r/overlanding

Amazon has them I believe.

I like this design as you could even put one of the van tents attached to the back door a sitting area. Pretty sweet.

Edit:. Here are some 36" 500 lbs ones. https://www.amazon.com/Drawer-Slide-Extension-Heavy-Capacity/dp/B0009OBPH4/ref=pd_sim_sbs_328_2?ie=UTF8&dpID=31jBKOPgl7L&dpSrc=sims&preST=_AC_UL480_SR480%2C480_&refRID=XQDMWSYA2V0GB3H6Q8G4