Here is what a dual stage looks like.
http://www.amazon.com/HUMMER-COMPLETE-AIR-SUSPENSION-COMPRESSOR/dp/B003P5BP9W/ref=sr_1_1?ie=UTF8&s=automotive&qid=1276051210&sr= 8-1 As for the programming, if you can still find a HUMMER dealer (???) they should be able to run the VIN and tell what has been done to the truck, I'd think ?
Ed
P.S. I am one who elected to convert mine to coils so not to have problems with the system that kept cropping up on me.