Front air ride suspension??

[Chamberpains]

Sounds like you have a couple of things that need attention. If your springs haven't been replaced and lived a hard life, I'd be looking to replace them along with the bushings.

Cab suspension parts wear out just the same as anything else. It maybe time to freshen up that area.

Leveling valve's almost always have adjustment of some sort. But even if it doesn't they wear out. Become sloppy and not as reactionary as they should. Have you ever replaced the air bags? They may not leak. But they do become stretched and worn from every day use. They won't rebound as good as they should and hold the weight like they should. Along with torsion bars and trailing arm bushings. These all wear out. Just because they aren't completely shot and broken doesn't mean that it's not past it service life.

At 739,000 miles, your truck has seen a lot of wear and tear. Most parts on the truck aren't rated to last that long and perform at peak levels. You might be surprised how sloppy things get in that amount of time. A lot of little worn out parts, compound in to bigger problems like uncomfortable rides.