Go with a 3500 diesel and never worry about it.
I just bought a new 17 Ram 3500 Tradesman nicely optioned CC 4x4 Cummins with the Aisin trans for $44k.
I have close to 4K lbs of payload and more power than Ill ever need.
If you get the 68RFE trans which will be more than enough for your needs, you could probably get it for $41k or so. Probably less $ than the Nissan.
As mentioned, the exhaust brake alone is worth going diesel.
The Lance 650 is also on my list of TCs.
The air assist may be nice but not required.
With the leaf springs just get the Stabil Loads if needed.