I have an 83 GMC 2500, yes I am running it on biodiesel. I am using a stock fuel filter, from NAPA. In fact I have never read of fuel filters (or any other filter) being and issue with biodiesel. Now if we are talking about waste vegetable oil, a stock filter can plug up fairly quickly and, as I understand it, some people are using filters with a larger micron rating. Personally I don't think that is a good idea. (For some people absolutely free fuel is hard to resist though.)