Right I've managed to have a measure. The 06 chassis is 44" wide at right behind the cab. On the 48 cab, I've got 49.5" between the rocker panels so the cab would sit over the chassis.
According to GM upfitters, the body on the 06 is 77" wide fender to fender. The 48 is 75" wide fender to fender so not a million miles away.
