[Diesel_Dave]

Well, I've done 2,360 mi in my truck with only one fill up (my last 2 tanks). However, I don't meet all of your guidelines:
1) My truck is a diesel
2) My truck is too new (2007)
3) My average speed is less than 55mph
4) My truck, as is, probably could meet the emissions specs from the 90's, but some of my mods may or may have altered it's ability to meet '07 specs, not that I'm admitting anything.

But I also had a few things working against me, most noteably the fact that most of those miles were 25 miles at a time (commuting), and I know I could do much, much better if I were driving without so much cold-engine time.

All that being said, welcome to Ecomodder! I look forward to seeing what comes of your project.