Just to finish off this thread:
Although I was seriously looking at the gasoline engines, they reduced the capacities of these trucks. The gas engines would be sufficient for what I currently haul and tow, but my future requirements will be higher and would be pushing the limits of the gasoline engines can offer. The chassis cab trucks run engines that tuned less aggressively than the pickups, so you must look at chassis cab specifications when comparing and ignore the hype about the latest pickup tune that one-ups the competitor.
This led me back to comparing the the two 6.7 liter diesels and their matching 6-speed automatics. I had very good luck with the 6.0 PSD and 5R110 in F250 and have always like the cab layout looks of the Ford. This put the Cummins with the Aisin at slight disadvantage from the onset, but I always judge companies on their current merits verses their past accomplishments. The Powerstroke has had issues with some Bosch parts that did put question in my mind but the fact Ford is now placing them in their Class 6 and 7 trucks gave me some confidence that they have resolved or mitigated the problems they had in the past.
Ford has been in the chassis cab market for a long time and has reliable platforms that pretty much dominate the the Class 4 and 5 market since GM dropped of it. If you need an upfit for a Ford, almost everyone will have multiple options from which to choose. Ram has only been doing this since 2008 but was lucky to get to some help from Freightliner which spawned the Sterling Bullet line as well the Dodge chassis cabs. The fact that most chassis cab accessories are based on standard frame rail width cab to axle distances does give you some choices, but there are some items that might have fitment issues due to varying placement of fillers and suspension hangers. Dodge's choice of using the Magna Steyr front axle without manual locking hubs left some doubt verses the tried Dana's in the Fords. I have not tracked any issues with the Magna axles, but Ram did upgrade the front suspension to a 5-link recently.
I was looking at the base trim models without all the gadgets and fobbles now being offered yet still wanted comfort. The base cloth seats in the Ford have a lumbar support and you sit more in the seat with side bolsters. The Ram only has slide and tilt adjustments and has more of a flat cushioned seat. Although both interiors look similar inside, Ford has more cushioned rubberized panels than Ram making it feel richer than the latter. Both offer power windows, cruise control and upfit switch options but the Ram came with better base radio and driver information panel than the Ford.
In the end, I had slight bias to the Ford due the availability of an extended cab, dual tanks and Dana 130 axle in a 60" CA chassis. The Ram won out on price, better instrumentation and less worry about the Bosch 4.x fuel pump issues. I ordered the Ram 5500 with Cummins and Aisin just before Labor Day and took delivery at the end of October.
The following day I drove the Ram home, I sold my F250 to a private party. It had been for sale since September, but the timing couldn't have turned out better and I think both me as the seller and the buyer got a good deal verses either of us using a dealer.