2004 Toyota Tacoma trips the cut off on gas hose pumps even when tank will take 10 gal to fill. To fill tank you must keep on pulsing trigger getting .04 gal or so on each squeeze.
If you are in the habbit of topping off the tank, by trying to fill past the pump shutoff, you may have saturated the charcoal cannister, which is part of the emmissions system. Hope it’s something else, since cannister replacement is around $400. Ask me how I know!
On the filler neck there is a check valve with a tube-hose that goes to canister if valve does not work or if hose is pluged or kinked that could be problen.
There are several possibilities inside the gas tank: damaged filler tube; a vent valve inside the gas tank not venting from one part of the tank to another; a stuck anti-spill valve. Gas tanks are different from one make to another, and from some years to other years. Your mechanic needs to know the SPECIFIC internal construction of your gas tank in order to fix it. Guessing don’t count.