Yeah, what I've been reading online was that 285s are about the limit for no rubbing without cranking the keys and adding blocks in back. And let's face it, this isn't a fuel efficient ride.I run 285s on my 1500 with some front crank and rear 2500 springs. Pretty sure the 8 lugs take them with zero mods.
I saw one for sale a couple weeks ago that had something interesting though. Apparently gear vendors sells a double overdrive unit that's intended to be used as such. And it's meant to be used with 4x4. It wasn't something they had on their websites last time I was there but that had been a long time ago. Went there after seeing the truck and yes, it's a thing.
I guess you switch it on once up to highway speed. Couple mpg on a pig is a 15-20% improvement so you make your money back quicker.