I own a 2011 Chevrolet 3500HD Crew Cab Long Bed LTZ with single rear wheels. If I switch to the doolie wheels and tires out back, do I now have a big doolie with the same towing and hauling capacity? Are there any axle/frame/drivetrain or any other diferences between a Big Doolie and my 3500HD SRW? I'm not worried about the doolie bed fitting, I want an aluminum utility bed (lighter weight).
Most aluminum flatbed/utility bodies are still heavier than the fiberglass standard pickup bodies. Reality is, you will still be heavier in the end with a aluminum body.
As far as gvwr goes, some say you can not change the door sticker, others know better, ie if you find the right body manufacture, chassis upfitter, they CAN and will change the gvwr if approriate items are added etc.
Reality is, you will lose some performance with a dually, as you will be turning more tires and wt ie additional drivetrain loss. The only thing you will gain, is potentially the payload part of the equation, which it sounds like you want. You could also go to some 19.5 SW tires, and potentially not have the amount of drive train loss as duals would do, and still have more payload at the end of the day!
05 Chev CC D/A LS Dooley
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer
3 Single axle utility trailers
Your 2011 3500 should have a pretty good RAWR as it is. The hauling or towing number won't change much (subtract the weight) and that's it. Where you'll gain is payload amount with the extra 2 tires. With 4 tires on the rear axle you'll be able to carry your full AAM axle rating of 9350(IIRC) . The dual rears will support roughly a 6k pound load of pin weight and stuff.
Can't really gain load capacity with spacers / adapters. Those only add stability, and only id you use a rear anti-roll bar under there, too. Gotta change the whole axle assembly, the dually version is wider.
Since you're swapping anyway, you can do a Dana 80, which has ratings up to 11,000#
'06 GMC C2500HD RCLB gasser 4.10:1, 4L80E, custom camshaft
'84 Trans Am 6.2 diesel, 700R-4, custom Class-3 receiver
'69 F350 dually. GM 6.2 diesel, turbo, 700R-4, NP208 all pending.