ok so serisousl is it possible to get a cummins 5.9 installed in something and actually get some decent MPGs - i'm talking a minimum of 30 or above, essentially i want a cummins vehicle that run awesome mpg, even if it sacrifices power, I figure that if banks can build a racing truck that's 735 hp still gets 21.2mpg why can't i assemble a vehicle that can atleast get 35 mpg?

or here's another thought - just 25 mpg and atleast some respectable power, the engine would more likely be put in something other that the 3500 it sits in currently, small vehicle, lots of power for weight and most importantly mpgs

 

What about a 4 bt?

 

I've never heard of a 5.9 getting that kind of mileage but a 4bt is capable. The guys over on ww.4btswaps.com can tell you more. They do a lot of jeep and ford ranger swaps but I've seen a few 1/2 ton and larger pickups and suvs.

 

I put a 4bt in a dodge 1500. I get 29 to 32 around town. and probably more than 35 on the high.
Yes there are certain things that you can do to get better mileage one is keep your foot out of it as a cheap one. But one that will cost you some money is go to gearvendors.com. The sell what is basiclly an extra overdrive for your trans. (not cheap). Another place to try and find mileage tips is Deiselpowermag.com They will have things form cheap to expensive to get you better mpg. But I thing that 30mpg is a strech, maybe 25.
Another thing to you go on long trips at a time. (45mins or more) that is also when you will start to get your best fuel mileage. Because the injection buy then is nice and hot and thins the fuel out and will spray less through the injectors.
I think that the 4bt is your best bet if you are welling to do the work.