I'm having a problem with my fuel system. After I shut down the truck from using my secondary fuel system. I believe the tank located up in the toolbox is draining into my main tank via the return line. I verified it's draining by removing the prefilter before the pump on my secondary fuel system. I was able to watch the fuel level drain down in the clear filter. So much so, that fuel leaks out of the main tank because of overflow. It's also being a pain to crank at times on either fuel system. Sounds to me like the overflow valve is shot. Anyone have any suggestions?