If it was effecting the gauge then it would of had to effect two electronic sending units, one before the filter and the other after the filter, not likely but could happen.
Not trying to discredit biodiesel, I remember the same thing happening when gasahol or ethenal as it is called to day came out.
I also use to be a farmer and still own a small farm, so anything agricultural related would be a good thing for me, I was just passsing on what I experienced and what others told my daughter when she worked for cenex. I do know that anything thicker than regular #2 will effect these lift pumps. When it gets cold around here the pressure drops and running straight #2 in the winter can take out a lift pump. I have replaced 4 lift pumps in previous years because I ran straight #2 in the winter. Last year I thought I was going to have to change the lift pump again for th e 5th time, I switched over to a blend of #1 and #2 and the lift pump has survived for a year longer so far, only time will tell how much longer.
I'am not trying to say all lift pumps or even anyone else's will do this, I just know what mine will do and maybe give people a heads up on something to think about when they have lift pump problems.
Ron