I bet that Ford Ranger would sell if it came with a 4 cylinder diesel standard and got close to 50 MPG. I am really jones'ing for a Volkswagen, probably a Jetta with the TDI .
I had a 1979 Volkswagen Rabbit Diesel that got an honest 50 MPG. It was not turbo charged, and really lacked power. I got rid of it before we moved out here to Arizona because it didn't have A/C. A/C wasn't offered in the Diesel Volkswagens until the 1980 models.
I looked into a new Jetta TDI but I backed off because there appears to be an issue with the fuel injection system in the newer models. It's a $7,000.00+ repair if it happens out of warranty. Several people have had problems. My 1979 Diesel ran perfectly for over 120,000 miles. I think if I was going to get a new truck today I would go with a Dodge Cummins Turbo Diesel. I co-worker has one that gets 28 MPG on the highway, and has close to 200,000 miles on it with zero issues. 28 MPG in a full sized truck with great towing power is a good tradeoff.