You will not get a factory 5th wheel prep package in a 2500 truck older than 2014. The frame redesign for the 2014 model year brought in the rear coil springs, and factory mounting locations for 5th wheel pucks and gooseneck hitches. The frame redesign was available in the 2013 3500 trucks.
If you're open to older trucks you can also consider the B&W turnover ball and companion 5th wheel hitch to give you similar function to the OEM 5th wheel prep.
My truck is a 2014 and I bought it in the fall of 2015 with 72,000 miles on the odometer. That's well over normal mileage but I haven't had a single problem with the truck.
