My 04 Avalanche will not let me fill the gas tank as the fill nozel keeps shutting off as I have now tried to fill at 4 differant pumps. Yes the tank is near empty but I can hear the gas coming up the fill tube as if it were full causing the nozel to shut down. Could there be a vent tube clogged? There does not appear to be anything in the fill tube but I can only see about 6" into it. I did put a flexable grabber down the tube about 2' but came up with nothing. I don't think anyone would have put something in my gas tube but cannot be sure. The truck runs fine as i have had from new and now have 105k miles.

Is there a check engine light on? The first thing I would do is look at the vent solenoid. GM has had issues with these either sticking closed or the filter getting plugged.

Find the charcoal canister. It will be mounted near the fuel tank. There should be a large hose attached to it. On the other end of that is is the vent solenoid. Remove it and see if you can fill the tank.

If you can than see if you can blow through the vent solenoid. With it unplugged you should be able to blow through it easily. If you can't than it is broken and needs to be replaced.

I beleive GM has updated the part and routing for that year. You can check with the dealer to see if that is the case.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

My Avalanche does this. Here is my cheap fix. When you put the gas nozzle into the truck, turn it towards the back of the truck and hold it there while filling. Now it is sideways instead of up and down. Changing the angle of the nozzle seems to work. This means you can't walk off and go wash your windshield while the truck sucks down 20 or so gallons of fuel, you have to stand there and hold it, but its cheaper than replacing a part, or it will at least let you fill up until you get it repaired/replaced. I have been doing mine like this for over two years. Just my opinion though.