When you say regular tune I assume you mean with the stock tune. I'm not sure it can be done with a scan tool but even if it can be done someone would have to know what they are doing and I doubt many techs do. It is not nearly as simple as changing from shift point A to shift point B. No dealer would agree to do it anyway. They will only load an updated tune file issued by GM. Before I got my tune I complained to the dealer about how it drove and shifted and got the standard "it's normal" answer.

BTW before I got my 2011 Tahoe I had a 2002 Yukon with the 4 speed. It shifted just fine and I was very happy with it. This was my reference point and why I hated how the 6 speed shifted so much. I knew it could be much better and now it is.