Here in Albuquerque I see tons of nice used tow rigs for sale along the road and languishing in the used lots (lots of peoples daily drivers that probably never saw tow duty). I see no point in buying new when used prices are dropping to crazy levels.
Also why the GM loyalty when you are having tranny problems with your current GM? (Everything I hear about the Duramax/Allison Combo is good though)
For Pros and Cons I would try the...
www.62-65-dieselpage.com