You should be able to tell if they're getting air- when you start your rig (at least after sitting for a few hours at least), go stand back by the driver side rear and listen for an air compressor turning on and running for 10-15 seconds and look at the fender to see if it raises up a bit. It takes maybe 20-30 seconds before the compressor starts to run after you start it up. You can also release one of the air lines from a shock ( with the truck off) and see if any air comes out and your rig comes down. Then plug the line back in, start it up and see if it raises back up.