Got a 6.2 raptor. What a screamin demon. Rear locker, big stock tires on 17s, huge suspension travel, and 400+ hp/420lb-ft. It has no problem with wonky terrain and steep angles. Different shifting, traction, and abs modes for different driving situations. And it loves mud. Best farm pickup ever.
From what I've heard, they didn't offer the Cummins in the Power Wagon because the intercooler won't fit with the big winch they have behind the bumper. Pretty lame reason, but its what I've read (somewhere?).