If there’s any way you could find one with the Cummins that’d be the way to go. Those engines last forever. I pull with a new 2500 and it’s like there’s no boat back there. I get 21+mpg on the highway without the boat or horseys out back.
The transmissions they’ve used over the years have been pretty standard fare.
The rough ride in a 4×4 is usually due to the solid front axle. Live axles ride rough but are arguably more serviceable (and infinitely more desirable for offroad, but that’s not important here).
I got hooked on Dodge trucks running them on the fire department and mainly like them for the Cummins.
You’ll be more than fine pulling it with a 318. There’s a reason why that’s been a great engine for a lot of applications (jeep grands, others).
LAXPatrick