I have always been under the impression that turbo's help diesels get better mileage because they help the engine breath - assuming you don't keep the pedal to the metal - but I read an article on converting a Toyota pup to a diesel that said the opposite.  What is your experience and knowledge about this?  

Doesn't make much sense to me.  Without the turbo, chances are you will use fuel that is not getting burned all the way.  I bought my truck a few months ago and figured I'm getting 15 mpg.  A few days ago, I found out that I've been running with the wastegate open. Its almost as bad as running with no turbo.  I still got boost, but only with the pedal to the floor and not until about 1700 to 1800 rpm.  I fixed the problem and filled my tank. I'll let you know what my figures are with the turbo working properly.