The dealership is full of crap and can tell you if it has been tuned. I would bet it has been tuned because of the way you are describing the shifts, the speed, and the AFM. Now you mentioned re-gearing, well let's hope so, if not that just sucks, and if you tow that really sucks. A 6in lift on 35s and factory gears is just wrong and so much of the truck is lost. If there is one more thing you do to the truck let it be a re-gear if it has not been already and it you do 4.56 unless not ever or not much towing then 4.10 is ok.