My best guess on a slight increase of value is two facts:
Megacab's are a bit rare of a truck to find. Drives up demand, same truck in a quadcab configuration of 5-8k less depending on options.
Second is new truck prices are INSANE. My truck, priced out today with the same options tips the scale at $75k msrp. With mine at 35k...I can and do see the appeal on the used market.
As for def lasting only 100-150k, haven't heard or read that but interesting to note for sure. Could have an effect on things. I'm not shy about the emissions equipment that fell off my truck....so I'd soon delete a DEF truck before putting in a 6k system after warranty is up. I'll read more about that.
Posted above about different rear axle weights for different gearing is true. The 3.73 and 4.10 drw trucks get a 11.8" or 300mm rear axle to handle the increased torque of the 900 and increased towing/payload of those trucks.
Wayne...your point is valid...what do I gain?