Jerryleejr,
He is looking at the DRW which is only available in 17" skinnies. The on/off road tire package is a nice addition which is available on the SLT and not the Tradesman, but if the OP is looking to swap to 19.5's anyway, he should check out the Tradesman trim and see if it works for him.
If you are looking at 19.5's from the factory, and buying a DRW anyway, why not look into adding a bed onto a 4500 chassis cab? Should be similar in price when all is said and done and you'll gain another 2k in rated GVWR.
That's crossed my mind more than a few times; however, I'm going to be pretty close to the 14k limit when all is said and done and I think I'd rather run the dual rear E-rates at 80-psi rather than worry about commercial tires and their high pressures.