I have filled avoiding the foam aw well... I even went and got a 2 gallon gas can to pour it in. I know I have less than 2 gallons in my tank and even with the gas can one gallon is all I can get into it before it backs up with no foam at all....
How do you *know* how much fuel is in the tank?
I've been tracking fuel mileage closely, so I always fill until clear fuel touches the visible weld line in the fill neck, about 8" below the cap. The process is a bit fussy, as I have to let the foam settle, and foam/fuel do "glug" out of the overflow on the side of the fill neck at times. But I let the foam settle and add slowly until I get clear diesel lapping against that weld line. That's my reference point for consistently filling the tank to the same point, so I can calculate MPG. I use car pumps, I've not tried the bigger truck pumps, but the goal is the same.
I fill up when the gauge reads 1/4 tank, and it takes about 15 gallons, so my gauge seems accurate. Many are not.
It's tough to imagine a circumstance where the truck runs fine and the tank won't accept fuel. Maybe if kids filled the tank with golf balls or something as a prank...
If you fill until you get clear fuel to that weld line, drive 75 miles, and it only takes 2 gallons to refill to that weld line again, that makes no sense. 37.5 MPG isn't in the cards for CUCVs. If you're relying on the pump shut-off or the fuel gauge to tell you when the tank is full, don't.
Please get back to us on exactly how you determine that the tank is full. It may be time to drain the tank, drop it, and take a look inside...