1991 F-250 7.5L engine, gasoline dual tank vehicle. Truck drives normally on the mid-fuel tank, switch to the aft tank, and after a mile or two, the vehicle loses power. It can still run if I stay under 45 MPH or so, but add more accelerator, and it chokes and stumbles from lack of fuel pressure. Switch back to the front tank for a few miles where I have full power, then back to the rear tank, and again runs for a couple miles, then abruptly gets starved for fuel. Only thing I have done to try to remedy the problem is replace the rear tank's fuel pump.

 

It might be a venting issue. Does the truck run with the gas cap off on that tank?

 

Thanks - I'll try that...