I don't personally have a STS yet, but when I talked to Allen about it a couple months back, he suggested I get one from these guys.
http://www.snowperformance.net/
From what I can tell, they make an awesome system and I will be purchasing one when I get my turbo.
FOR ALL YOUR WHEEL, TIRE, AND ACCESSORY NEEDS
CONTACT: EPLEY'S TOUCH OF CLASSIC 1-270-843-6892
OR TO GET ME PERSONALLY CALL: 1-615-943-6514
2000 Chevy Silverado 4.8L RCSB: smoked UPD, Flowmaster exhaust, De-screened MAF, Nelson 93 hot tune. Upcoming installs: trans-go shift kit, Eaton posi, billet servo, ported and polished throttle body...Near future: 6.0/4L80E install with 150 wet shot