There is a couple of shouldered bolts on either side of the armrest, inside the plastic cover. Over time they will back out and kinda screw up the way that the mechanism works. Pull 'em out, put a couple of drops of red lock-tite on those, then crank 'em down. Sometimes the bolts that hold the armrest bracket to the seat loosen off too. You may have to remove the backrest from the cushion to access the bolts nearest to the backrest. You don't have to remove the seat from the truck to do this. Passenger seat all the way to the back, & the driver's all the way forward may give you the space to work in there.
To remove the backrest, flip the backrest forward, undo the long plastic clip, or zipper, & pull the cover up to get at the outer bolts that hold the recline mechanism to the backrest frame.
If there is a zipper in there, it will not have a pull tab. Work a paper clip or other piece of wire into the small hole on top of the slider. The zipper is self-locking & this will release the lock. Don't undo the zipper all the way. If that slider comes off the zipper, not only is it a pain to get back together, but good luck getting it back together so that it lines up again to the way it was originally put together.
The inside hinge of the backrest is on a pin, inside a plastic grommet, which fits into a bracket with a corresponding hole in it for the pin. IIRC the pin may have a tooth on it which is on an angle. You have to play with the backrest a bit in order for the tooth to be removed from the hole. Lift the outer side of the backrest towards the center of the vehicle, while rocking it around to different angles to get that pin out, while pulling the backrest towards the outside of the truck. Once you have the backrest off, you'll see how it works.
