My '06 isn't bad if I keep my foot in it. Towing 6000 lbs and I can't say I have had this problem, but my fuel mileage isn't the best either. lol. I do notice that if I have any hills to navigate that I do need to turn off the AC so it doesn't bog down, but that is the only time I have noticed it and it's due to engine load rather than transmission settings.
An upgraded valve body will help out to firm the soft shifts the tranny has. It was designed to be soft as most owners do not haul much with these vehicles and want the more comfortable settings. The owners on this board are a different story though!!
