My other philosphy is go to the local dealers and poke around at used trucks - drive a few (Ford, Dodge, GM) and get a feel for them, see how the interior lay out is, pick the design/body you like best then start some serious shopping.
06-07 Classic GM, LBZ Duaramax, which has the 6 Speed with manual mode is a great truck. I'm unsure if that body style existed as a 3500 SRW though.
I recently drove a 2013 dually Dodge (er... RAM) and it rode rougher than my GM Dually. I blame it on the solid axle front suspension of the RAM. No biggie if it's loaded, which would smooth out the ride some, but I drive my truck empty some and the Cadillac style ride of the GM IFS has spoiled me.
