Gas tank won't fill completely full
 

Since buying this truck a while back, it would never fill completely up, or so the fuel guage says. When I first filled it up, it needed a new fuel filter gasket. I knew it was an issue because fuel would spill out onto the ground. I thought that was the problem. It still only shows half full on the fuel gauge.

I'm not sure how to attack this.

If it overflowed through the fuel filter hole when filling, it was pretty close to full, correct? Maybe not. I don't know. Common sense says yes, but I really don't know.

The other possibility is that it is filling to full but the fuel gauge isn't reading it right.

How do I find these things out? Is there a way to see a reading on the fuel tank or on the fuel gauge? The engine and transmission are out, so no using normal power. I could feed it 12v power if needed for testing.

Has anyone else encountered this before?

it's probably a float in the tank issue' but try filling it slowly and see what happens.
my truck will stop at 20 gal. if i set the pump, Now if i stand their and fill it slowly it will take 25 gallons.
I'm sure mine a vent problem. but not enough of a problem to fix.

What he ^^^^ said.
I've had that problem before and like drowssap said I had to fill it slowly to get it full. I ended up disconnecting the vent tubes and blowing them out with air really good and I haven't had the problem since.

I started by disconnecting the purge valve and following the line to the charcoal canister and disconnecting the 2 vent tubes going to the canister. Then follow the 2nd vent tube from the canister back to the fill tube and disconnect it.
Attachment 22072

There is also a vent tube going from the tank to LVS that I disconnected.
Attachment 22073

Once you have all of the vent tubes disconnected blow air through each tube and have someone at the other end verify that a good amount of air is coming out. When you blow air into the vent tube going into the tank, listen to the tank and make sure you hear air going in. Sometimes bugs can build nests or dirt can build up and restrict the venting of gas fumes.
I may have forgot about a vent tube somewhere but you should be able to figure it out. You get the idea, Find all the vent tubes and blow them out.

Vent tubes can clog from dirt or collapse with age, should not vent out filler tube.