What suspension are you using for the weight?  OME?  I'm just finishing up my alu cab build out, and I'm sagging quite a bit.  Unfortunately not a lot of spring options up here in Canada.
		
		
	 
I run a 3.5" Fabtech spacer lift kit utilizing the OEM front coilovers and rear dirt logic shocks. I have 1/2" of sag in the rear that is barely noticeable.  I purchased the truck with the kit installed and everything is covered by warranty.  I am running up on 70,000 miles and have never been turned away by the dealer on any warranty work.  The Project M weighs 352 lbs and I travel light: two Ridgid drawers, a Ridgid case, two FR wolfpack boxes, and a 20QT cooler--no fridge, nothing fancy.  Keeps me nimble and adaptive.