Re: $1,735!!!!!!!!!!!!!!!!!!!!!1
For passive replacement, the aftermarket options seem to consist of Strutmasters, Arnott Industries, or Boston Suspension. Each claims to bypass the ride control system's safe mode (90 mph limiter). Not wanting to seem biased, I'd suggest you run a thread search on these individually and develop your own opinion before purchasing. It seems that some folks haven't had the best luck there. Entire kits seem to be in the $400-$600 range for all four corners. Obviously you'd need to pay for installation if you arent a do-it-yourslf type. I'd guess that would set you back $200 - $300 at a suspension shop.
Other passive options are available for less money, but you'll need to trick the ride control computer to avoid RSS codes. Krashed has a clever idea whereby he recommends carefully removing the damping valves from the top of the original struts/shocks, bagging them off and tying them out of the way to avoid codes. He says this is working for him.
If you want to stay factory, buy the shocks from GM parts direct and save some $$$. Two rear OEM air shocks (GM part #s 22064872 and 22064873) should set you back about $432 each with shipping/handling. Any suspension shop should be able to install these for well under $100 - it's about a 60 minute job - max - with shop facilities and air tools.