You might consider super single tires with a much higher than stock weight rating. Look at a place like
http://www.ricksontruckwheels.com/index.phpThey sell 19.5" rims with a 4,500 pound weight rating, and you can buy tires locally to avoid shipping fees.
If you have 4 wheel drive, then replacing all the rims is required to keep the same outside tire diameter. If you have 2 WD, you can just replace the rear two, and keep the others for the front axle or a spare. Sell the tires once they are nearly worn out on Craigslist to recoup some of your investment in the larger rims. .
Aftermarket conversions usually require a hub being installed to offset the front rim by 4" outward, to fit the dually shape rim on it. And the same type of adapter on the rear axle. Both are somewhat 'weak links' that I would rather not have on a 10,000 pound truck!
Good luck!
Fred.