Well I have an experience. My pops '03 Trailblazer does a bunch of towing so I figured I'd drain the entire system and refill with the Supertech Dex VI that is in question here. He's still under impression that all tranny fluids are meant to be in there the lifetime of the vehicle.
I always used the Warren ATF+4 stuff before from Wally-world so figured this Dex VI would be better then not changing the fluid at all.
After draining and filling then test driving I noticed no real major change in shifting characteristic. Perhaps crisper shifts but that may be my imagination. I did not do a uoa on the old Dex III that was in there, so I do not know the condition of old fluid. Unit had 43K on it with at minimum 170 80-mile tow trips overall. Trailer weighs in around a little over a ton. Condition of old fluid looked good, was a deep red with no noticeable metal debris.
The new Dex VI fluid has been in there for only 1K so far, but the unit shifts and drives like it always has in the past. I will see what happens in the next 40K.