Air Suspension - Variable?

[CO Hummer]

When I first upgraded my tires to 37s, the H2 fit fine in the garage with 40psi in the rear. After I went wheeling last Saturday, I drove into the garage and cleared the front (which clears the highest part of my Gobi rack). But the rear and of the garage hit the trim as rolled through. When I shut it off, I could hear the rear release a ton of air. I backed out the next day, no problem. Then after a short pavement based drive the next day - it hit going in. The next morning, it hit going out. When I pulled it in last night - it went in just fine.

I just don't get it. Why is the rear height variable?

All the times going in and out of the garage I had the same weight inside the truck yet the rear height varies by about 1.5 inches. Isn't there a sensor that is supposed to put in a predeterined height?

Time to take the trim off the top of the garage door.