Keep in mind that doing this will not increase your cargo capacity. The limitation being your axle. Check the stamping on the axle, IIRC it's not a 3500# axle, but something like 3200#. They've changed them from year to year so best to double check.
I always ask out of curiosity, what problem are you trying to solve by doing this?
2013 Jayco Jayfeather X20 E, 2008 GMC Sierra 1500 Crew Cab Z71 SLE