You will have a 6L80E. It and the 6L90E are the only GM-based longitudinal 6-speed autos in GM's line up. The 6-speed autos behind the diesels are the Allison 1000.
This is a direct clutch-to-clutch transmission, meaning there is no hydraulic over-lap and accumulation like in the old 4L60/80e transmissions (same for other auto maker's trannys). There probably will never be any boxed "shift kits" for them. ALL the shift timing, pressures, accumulation, and circuitry are totally controlled by the TCM through a sort of hydraulic/mechatronics control system. Any real "kit" is going to have to come by way of careful TCM programming, keeping in mind whatever stock or non-stock parts are in the trans. That's the difficult part though... all it takes is a couple of thousands of a second mis-time and you will get a bind or flare during the shifts.
There are some upgraded red-lined clutch packs (with more frictions than stock added) appearing. The most developed version I've seen is from Circle D in Texas, as they are having some new reaction carriers made to take larger clutch packs. But these will need a tear-down to install.
There are ways to modify the hydraulics in the hyd/mech control system in the trans, but it should be left to someone with a LOT of experience. It's quite complex and I don't foresee an off-the-shelf solution for the average DYI'er.
Have a tuner take conservative steps over the course of a few re-loads. After a couple of tries you should get to where you want it and not destroy the trans in the process.
When done right the A6 transmissions are very impressive. I got to see one in a Pontiac G8 that had a little work and it was an amazing performing trans and almost matches the fun-factor of the manuals.
