It is always a trade off. One of the major factors of a gas performance tune are the shifting characteristics. Increasing line pressures, shift points, etc is part of building a performance tune and because no two people or driving styles are the same, you will always have some folks that the performance shifting strategies work for and others that it doesn't. A performance tune with the factory shifting strategy will never yield the same responsiveness, etc.
Also, I will add, I shift mine manually most of the time, especially around town. But I do so without putting the shifter in actual manual mode position. You can be in automatic mode and lock out whatever gear you want. I have found that this causes two different conditions. First, if you are in auto position and lockout 5th & 6th gears, it will hold 4th gear pretty much to the rev limiter. But, at the same time, it keeps mine from "searching" for the right gear to be in when at that sweet spot of shifting. I have not had trouble with doing this and in fact, the only trouble I have had with my tranny has to do with another common issue with the 6R80 tranny where it may (from a dead stop) shift all the way to 5th gear on it's own and you have to turn the truck off and cycle the key to reset everything. (I am currently waiting on the dealership to call me and let me know the parts have arrived so they can fix that, but it is an issue common enough with stock tuning that there is a factory TSB about it being fixed under warranty)
