For farts and giggles, was doing a search on F350 dually's ('17, '18) and from what I'm seeing, they don't offer a 3.73 ltd slip rear end, just a 4.10. Funny how dealers don't order this type of truck...
We bought our '17 King Ranch, with 5th wheel pkg and all the other bells and whistles, for a bit over 60k last fall. I do not know off the top of my head which rear end it has though. We did get a killer deal on it, as it was end of model year. MSRP on the sticker was almost 80k. Not sure that's the norm though, but we were happy with it. The other part of the deal that worked well for us was that they gave us 53k for our trade in, which was a 2015 DRW Platinum, with only 13k on it.