When trying to fuel the truck, gas leaks out when getting towards a full tank....everytime. anyone know what could possibly cause that and how to check it. I'm moderately mechanically inclined so mostly able to do all on my own. Just need guidance.

leaking gas would show up somewhere --sure not being siphoned

Try slowing down how fast you pump the fuel in, the curve of the tank filler pipe and the stopper valve at the end of the pipe(in the tank)will act as a restriction causing a backup when filling too fast. Or the stopper valve is sticking in the tank. To fix that ,you would have to replace the tank.

Something is wrong with the float or the sending unit.Did anyone replace the fuel pump lately.

The most common cause for these codes are a bad gas cap the seal wears down after a while. It could also be the charcoal canister has a crack or is damaged.

A defective fuel pressure regulator (located on the fuel rail) may have blown the gasket on the
fuel pump (located in the gas tank).
Another thing to check - the car's computer may have posted
an error code from the fuel tank pressure sensor.. I'm not sure, but if this sensor shows pressure
building in the fuel tank, rather than let it explode its seals, the sensor may intentionally leak fuel
in order to relieve the internal fuel pressure build-up inside the fuel tank.

On the fuel rail (supplies fuel to the fuel injectors on top of the engine), there will be a Schrader valve,
which is your connection to connect your Fuel Pressure Gauge to your car's fuel rail.
Give it a check, but put a shop rag around the connector as your screw it in - fuel (and fuel
pressure) will leak as you install the fuel gauge.

You may get computer diagnostic codes P0158 or P0159 - see below for interpretation.
Note that the PCM is the Powertrain Control Module, which is the car's computer.
Also "TP sensor" is the throttle position sensor.
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Trouble Code: P0158

Meaning: HO2S-22 (Bank 2 Sensor 2) Circuit High Input

Possible Causes:

Fuel system is too rich (fuel pressure too high, fuel pressure regulator leaking, or one or more fuel injectors sticking/leaking)

HO2S element is silicon, water or fuel contaminated

HO2S signal circuit is shorted to system power (B+)

HO2S signal tracking (water intrusion) in the connector causing a short between the HO2S signal and heater power circuits

PCM has failed

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Trouble Code: P0159


Meaning: HO2S-22 (Bank 2 Sensor 2) Slow Response

Possible Causes:

Exhaust leak present in the exhaust manifold or exhaust pipes

Fuel system is too rich (fuel pressure too high, fuel pressure regulator leaking, or one or more fuel injectors sticking/leaking)

HO2S element is silicon, water or fuel contaminated

TP sensor element broken (can cause false acceleration event)

Your vent pipe which allows gas fumes to come out of your tank as you fill it sounds like it's not working.Did this just happen and if so have you had anyone working on your vehicle near the fuel filler?

go to a muffler shop and hve the system tested for leaks, don't take chances, the gas guage issue is caused by the fuel tank sending unit being defective.

This is a common problem. On the driver's side frame rail is a large black plastic assembly that the fuel lines connect to. This a fuel switching valve what usually happens is the valve goes bad and the fuel gets pumped from one tank to the other

It is the filler neck it causes splash back.

hi there well it seems that you have a problem with our sending unit in the gas tank maybe someone replaced the fuel pump and they replaced it with the more affordable aftermarket one or its also possible that the mechanic that installed this pump inside the tank danaged or bent the fuel float leaver you will have to dropp the fuel tank down or look for an acess hole under the carpet in your van and open tank and inspect for damaged float system try bending the float leaver wire down towards the bottom of the tank if this doesnt help the problem , you will have to install another sending unit without the fuel pump a little adjustment will do it though, ok hope this helps you a bit