Just needing some help. My 2004 3500 seems to be serging at around 70 mph only when I'm lightly steping on the gas. Doesn't seem to do it other than at high speed. Just currious if this might be my fuel pump or something wrong with the fuel system. If any one can help?

 

First thing that comes to mind is the FCA ( Fuel control actuator). You might want to start there!

 

I replaced my FCA for the surging issue and it did not fix the problem at all. Ran 50% bio and problem went away completely. Back to #2 and problem is creeping back.

 

Now I'd expect that result if you went from 50/50 back to 2, but from 2 to 50/50??? Where are you getting your 2?