I don't know what system was used back in 2002 but here is a picture of the system in my 2012.
As dieselguy suggested I would take the top off the bed to expose all the workings for the slide movement.
As you can see in the picture there are square tubes on both sides that act as a guide for the travel of the slide. There is an angle iron attached to the floor near the outer wall of the slide, this in turn is bolted with 4 bolts to another angle iron to which the tubes are welded and is driven by the ram. If yours is similar and some of the screws have come loose on one end of the angle iron it would not draw that end in correctly. This could also happen at the ram end of the mechanism where it is attached to the floor. Also the tubing on one side might be binding causing the slide to not come in freely on that side.
As dieselguy said, do not adjust the large nuts on the ram or you may create a condition whereby the slide tries to go too far out or too far in and you then would have bigger problems.
Not sure the picture will help but it will give you an idea of what things might look like under the bed.
My problem was the slide worked fine but went out and left the bed behind. Thanks to the quality workmanship of both Keystone and my dealer the screws had pulled out of the outer wall and the bed frame. I revamped the fastening system to the wall for the bed frame and fixed the castors the frame runs on as they also had twisted and the screws had come loose. Works great now.
Good luck with the fix.