2006 GMC Sierra 3500 Duramax. Decided to fuel up my "new to me" GMC. With fuel in both tanks I got home and saw diesel coming out of front tank cover. Upon inspection found the fuel pump did not shut off and was continuing to pump diesel from rear tank to front tank and would not stop. Was told it was 2 sensors that probably needed to be replaced. I replaced the one in the fuse panel under the hood for the front pump. I also purchased a fuel pump balance level relay hoping this would fix the problem. Opinions? and where is this balance relay actually located on the truck?