A good alternative to the current powerstroke would be the 4.4 diesel Ford is working on for the upcoming f-150. I imagine its going to be a good bit lighter, and its based off of the 3.6 diesel they put in the Landrovers across the pond, which get around 36 mpg's from what I've read about them. Only problem is you're going to be waiting a year or two to get it. Would be a sweet swap though. And ditto on beefing up the front end, regardless of what you put in it.

Will