Self level susp inactive

[CTSportX5]

For those who will scream use the search feature, obviously you haven't had to search this topic. There are what seems hundreds of posts and I wasted an hour trying to sift through them. Although I hate to add to them, I have narrowed down my particular case and am looking for a suggestion based on my symptoms.

Driving along last week this error randomly popped up on the cluster. There were 2 people in the back. I start up the car an hour later with only myself in the car, the fault is gone. I drive 30 min with no problem. The next day with 2 people in the back the error pops up again...so it seems to me the system senses the extra weight and wants the compressor to kick on, but the compressor never kicks on and the error appears. I have checked fuses and inspected all the wiring in the spare wheel area. All in order and dry too. During my search I read about the "air supply control unit" and a certain module that goes bad. I hate throwing parts at a problem not convinced it will solve the problem. Anyone have any insight for my particular problem?

BTW, it is a 2005 4.4 with rear air bags only. Thanks!

EDIT: Some extra info. The ride height seems normal (the bags are not losing air). It has felt a bit more harsh/ bouncy recently- probably due to the bags staying at a constant PSI..