For what it is worth, I have had nothing but trouble with fuel pumps etc. on my 86 F250 4x4. I put two new pumps in when the gauge quit. They have never worked right since. The rear tank pumps 5 PSI, the front pumps 1-3 sometimes. So I added a Carter Elect. Pump mounted on the frame with a Pres. Reg. ON/OFF Switch. Now I have little problem. I keep thinking I'm going to put about a 75 gal tank in the bed, and just remove all factory crap that has to do with fuel. Just run the Carter & Pres. Reg. 3/8" feed line and a 5/16" return line and the heck with all this trouble & cost. I think that your problem is in the switch over valve, That I believe is where some of my problems exist, and if I replace that at I think about $150 then I'll have over $500 in two pumps a valve and miscellanous hoses and stuff and if you add up the Carter pump, pres. reg, & Pres. gauge 6 bills is closer. Heck I could of bought a bed tank & gauge unit and saved alot of money. My point is this system has been junk and still is. I was working for a Ford Dealer in 84 and we worked on this system all the time. This must of been one of CHEVYS BETTER IDEAS, THAT FORD JUST COULDN'T SAY NO TO.