At this point, I'm leaning toward a 2015 Ram 5500 chassis cab crew cab with 60" CA (cab to axle length) running 6.4 V8 or a 2016 Ford F550 chassis cab super cab 60" CA running the 6.8 V10.
There are rumors that the class 4 and 5 V10 may get the 6-speed that is used in the class 6 and 7 trucks and Ford may go to an aluminum SuperDuty body this next model year - I have not heard of big changes on the Ram side.
The current diesels are too costly to acquire and repair for me to justify the cost over additional efficiency or capacity. Both gasoline engines have sufficient power and gearing to do what I need.