When you move the seat forward, after releasing the backrest, do you have to release the track with the handle under the front? Or can you move it as soon as the backrest is flipped forward without using the front release?
Seems to me that when you flip the backrest forward, the whole seat should slide forward without using the front release. There should be a rod or cable connecting the backrest release to the tracks, so that the one handle does both jobs. That will be inside the outer cushion cover. Have to open up the seat to access that. Gotta do this on the bench. You might be able to remove the plastic clips on the underside edge of the cover while the seats are in the truck, but you won't be able to get it back on.
I've seen mechanisms installed wrong, or not tightened down properly, or even rotated 90-180 degrees.
Sounds like you may have to pull the cover off to get at the mechanisms to see what may be broken, missing or installed wrong.
If the seats been messed with before there could be any # of things. I think that the big spring underneath the seat may be installed wrong. Common mistake of someone that didn't check after the upholstery job, either because of lack of time or experience.
If you are to work on this yourself, a couple of safety warnings.
Undo the front floor bolts first, slide the seat forward, then remove the rear bolts. Not only does this let the seat stand on it's own on the bench, but if you do it in the opposite (Back bolts first) the seat will flip & fall all over the bench, fighting you all the way, If you happen to hit the release for the tracks, the spring, when properly installed, will fire those tracks from one end to the other with such force, it WILL cause serious damage to your fingers if they are in the way. I mean serious damage! Broken if not removed digits!
The same goes for the backrest release mechanism. With the backrest in place, the weight of it will slow the mechanism down. Without the backrest, the springs will snap the mechanism forward faster than you can blink an eye. So, flip the backrest forward before you try to seperate the back rest from the cushion.
Let me know what you find. Pix? Questions?