Actually neither engine.
In the Dodge we are running the Cummins with an Allison Automatic. All cummins engines are only 6 Cylinders but they pull great.
The chevy, believe it or not is a 6000 series gas, not even the big block or the diesel. The reasoning for doing this was everything in the trailer is gas and we wanted to keep them identical to avoid searching for two fuel stops. It is a five speed. I always prefer to tow with a five speed to have more control and it does pretty good. The Chevy will pull away from the dodge off the line, but the Dodge will pass it by around 60 on the highway because of the torque. GM has a really good rep with gas engines and it really does okay pulling 10,000 pounds. It does 65-70 down the highway no problem. I wouldn't want to go cross country with it with that much weight but on 20 mile jaunts its fine.
Hope this helps.