would get a second opinion from Freeway Transmission, and if it really is indeed bad, I'd have them do the work.
They did my Firebird (I neutral dropped it and toasted it, none of this "subtle symptom" junk she plain well wouldn't shift!), and not only did they warranty and put in a good effort, but they installed an aftermarket transmission cooler as part of the deal, something that modders would spend hundreds of dollars to install on their already good trannys.
If you have a 2500HD, you should already have a tranny cooler (not sure about the 1/4 tons), but, I really liked Freeway's work.