The '08 model Ford diesel engines are equipped with some new "clean emissions" system which has a cycle in which there is a "burn off" of some type of filter in the catalytic converter (I think). I noticed the cycle right away during the first week or so I had the truck- it idles much higher (around 1200 rpm) when in neutral or park and all sorts of air sucking and blowing noises can be heard under the hood, plus the exhaust air blows from the tailpipe hotter and stronger.
It is only supposed to stay in this cycle for a few minutes, but I began to notice that it was cycling for longer periods and more frequently. During the cycle, the power from the engine is noticeably less and the mileage is terrible (about 8mpg). I brought it into Ford after it was stuck on for 2 days and I was worried that it was going to catch on fire or something. I did not acknowledge use of biodiesel to them until they asked what type of fuel I was putting in, and then I only admitted a blend of B25 (I did not want them to have a scapegoat on warranty repairs). They told me that biodiesel in concentrations of more than B5 will cause the burnoff cycle to stick and told me to put diesel in and it would stop. I ran about 1/2 tank of diesel through the truck and it came off it's cycle. I have not put any biodiesel in since and have not had any problem with the burnoff cycle.
I am sure that they would talk to you about it at Ukiah Ford. They seemed real sure that biodiesel would cause this type of issue with the new '08 emissions systems.
I am disappointed, and I hope you find something out. I was told that Chevy and Dodge are coming out with similar emissions systems when their '08 models hit the street.