From what I've read these trannies use a TCM (transmission control module) that is located inside the tranny. It talks to the ECM (engine control module), they collaborate, and decide when to shift, how hard, etc. These parameters are programmable using a laptop however I'm unsure which software companies support this, such as HPtuners or EFI Live.
Also, the engine needs to be a Gen IV with a 58x reluctor wheel for the ECM to talk to the TCM.
As for aftermarket companies with harnesses and computers to control the 6L80/90, both Mast Motorsports and Speartech have them.
http://www.mastmotorsports.com/2010/...ponents&id=290
http://www.speartech.com/