IMO, I would stick with the Ford. I think the truck is better built overall. The Cummins engine is a good one, but I think the 7.3 is solid as well. No doubt these trucks do feel doggy when stock, but a few simple upgrades such as an intake, exhaust, and chip will really wake them up.

If you feel the need to swap a Cummins in the truck, I would look into Destroked as someone mentioned. However, if you run the cost vs. HP of swapping in a Cummins versus modifying the 7.3, I think you'll find them to be very comparable.