I have an 06 Trailblazer Ext that I built a 5.7 for similar to an LS6. This is my daily driver so I emphasize comfort as well as performance. I dont normally pound on it, but I do use it to tow with a lot. I Recently had the tired old transmission rebuilt with upgraded internals, but I did not install a shift kit as I am not after neck snapping shifts, and the first trans lasted 180K miles without one. When I got it back, the 1-2 and 3-4 shifts basically felt the same as they were, which was a bit soft, but the 2-3 shift was really on the harsh side for me at lower throttle shift points. My re builder tells me it is because of the upgraded clutch packs we used that are a lot tighter clearance wise than the factory pack was. Here is what I have done since installing it to try to get it to shift more to my liking, IE so all the shifts feel similar, and with some success.
Besides getting the shift points where I like them, I raised the pressures a tad on the 1-2 and 3-4 shift and shortened up the shift times on the 1-2 shift. The shift times on the 3-4 shift were already set to zero from the factory. I am fairly happy with those two shifts now, and did not stray too far from the factory settings. They have a nice firm but comfortable feel.
To try to tame the 2-3 shift a bit the only thing I knew to do was to lengthen out the shift times. I currently have the shift times in my light throttle settings at about .450 whereas they were originally about .350. I do not know how far is acceptable to lengthen them. It is considerably better than it was but still a little harsh rather than simply firm. Is there something else I could adjust to tame that 2-3 shift a bit at low throttle settings? Can I continue to lengthen the shift time as long as it still feels firm? It all feels great when you hammer on it though! Thanks