ProStar Sleeper Suspension Modification...

[Chamberpains]

I would look at your cab leveling valve. If it's broken internally then it will not send air to bags.

Also make sure if you replace the leveler that you install it correctly so that it inflates at the right angle. Most leveling valves are pretty universal as to fit many different applications and mounting styles. It's not hard to wrongfully mount one to fill when it's to dump or vise versa.