could be you need a cross flow check valve added to your fuel line. There were recalls for this on 94's. See alldata.com, TSB's on the left and then find your year 0of truck at ther bottom of the page. On my 87 it was cause d by a fuel selector value going bad. Look up recall because sometimes it builds up pressure to in the tanks. Haynes says if FDM intank fuel pump is bad you need to replace it , no repair kits for a stuck valve inside pump .