Go Manual While You Still Can
As a ’14 2500 owner, I’d like it if my transmission was beefed-up, seems unlikely they have two, very similar versions of the G56 transmission?
The one turbo-diesel pickup I purchased with an auto trans was my probably my biggest automotive mistake ever... It was 1995 2500, and the chronically leaking transmission cooling lines and several other problems in the first nine months prompted Chrysler to buy-back the truck. This was after a '93 first-gen with a Getrag 5-speed that hadn't given me problems, but it wasn't old/abused enough yet. Had I ordered a manual in the '95 I would have received the cast iron-cased—heavy-duty but not problem free—NV4500, which was a relatively new and unproven design at the time.
The returned 1995 2500 fiasco lead to a positive a year later, with the ordering of a '96 F-350 with the ZF S5-47, the first year with the lower first gear behind a diesel, a welcome surprise for starting loads and off-highway crawling when it arrived. The ZF S5 was/is an aluminum-cased gearbox, and also known to run hot... so much so that the 6-speeds in later trucks included a cooler. I towed fairly heavy, mostly in overdrive because with 4.10:1 gears I needed it for reasonable rpm, including charging up hills, gross-combined-weight of about 16k. I had a temp gauge on the ZF and would see high temps 220-240+ depending on the load and conditions.
Early on I replaced the often burnt/oxidized smelling ATF oil with proper manual transmission oil, MTL from Red Line, which I also ran in the transfer-case. The transmission shifted so much better with good oil that allowed the synchronizers to work. That ZF only held about 3.5 quarts so I changed it at 10k intervals and had zero problems with the trans, just the dual mass flywheel (replaced with single-mass) around 90,000 miles. The truck had 133k on it when sold to a friend.
Now I'm the owner of a '14 Tradesman with a G56, and I just recently changed the gearbox oil from the ATF junk to Red Line MT-90. I'm looking forward to many, mostly trouble-free miles, confident the proper oil will help, and am prepared to change the clutch/flywheel after many thousands of miles if/when needed or desirable. The G56/Cummins combo is nice to drive, the shape and position of the stick is better in this 2500 than in the F-350.
Regarding power... In May I was only casually thinking about buying a new truck (but bought one in June) and at an event was talking with the owner of a Jeep modifying business that hauls a few jeeps on one trailer to gatherings like the Easter Jeep Safari (heavy!) with G56 trucks. He is a manual transmission fan, has a few G56 Cummins trucks and obviously uses them hard. His comment about the lower power rating was that "they don't drive like it". I'm still impressed with the amount of torque and HP my low-powered, 3.42:1-geared truck (I thought the gears would be too tall) offers if/when I want to stomp-on-it. There seems to be less toque-management. I don't baby it, when I want all-of-it, I'll floor-it, and I'm still impressed with how this stock G56 moves.
Attention: TDR Forum Junkies 
