What are you guys getting for fuel mileage on a stock Disco II? Ist there a company that sells a tuner, chip, programmer for these engines that works?

I run a programmer on my Cummins diesel and wow what a difference, more HP and Torque as well as better fuel mileage. Was hoping to do something like this on the Disco.

 

Nope, not going to happen.
Use the correct fuel grade, light on the throttle and be happy with the combined 15mpg.
If you want mpg buy a Jetta TDI or a Civic.

 

or ditch the 20 inch rims you put on your truck

 

Diesels leave a lot on the table in programming because they are tuned for their application, to not trash the driveline they are put in, and for warranty purposes. You won't find the same type of latitude with normally aspirated gas motors.