Fuel/running issues on interstate
 

My dad has an 07 FJ auto/4x4 with about 180,000 miles that has had fuel/running issues on the interstate. I live in SC and they live in WV. Every time they've visited recently the truck runs rough, sputters, and shuts off at least once during the 500 mile trip down (never back up).

The first time they made it 450 miles before it quit. Got it started back up after a few cranks and took it to a shop. Mechanic dropped the fuel tank cleaned it and replaced the fuel pump. They made it back to WV with no issues. Next trip down it started sputtering with a quarter tank left while going up a hill after about 300 miles. Got to a gas station, filled it up and no more issues. The rest of the trip they never let it drop below a quarter tank. This time they're on their way down and started having issues 150 miles into the trip and a half tank. Got to a gas station, filled up and are on their way again. Once they make down they're taking it to a mechanic again.

Of note; the is by dads DD, and he doesn't have issues around town or driving to work. It's only happened on the trip down from WV to SC.

Any thoughts on what the issues might be?

Thanks!!!!!

Man it could be a number of things, i'd have them check the ignition systems and check for vacuum leaks. Could be injectors or lord knows what. Yeah im not being much help here, sorry lol

The FJ has an issue with the fuel filter getting clogged. I need to replace the fuel pump and filter on mine, because even bone stock, I got 16mpg...

I'll be dropping the tank soon. Sigh.

if it's like the engine dies, but doesn't, while driving and when that happens you don't have throttle response... it could be a fuel pump relay. i troubleshot my fuel system problem on my accord and pulled the pump and bench tested it and everything and it ended up being the relay. if that relay starts acting up, you will get the exact same symptoms that a bad fuel pump will give you. for my 4runner, it's like a $6 relay.
i swore to myself that day that i would replace the relay first if troubleshooting a similar fuel problem. would've saved soooo much time!!!
i'm an electronic technician and understand relays and how much wear they take over long periods of time and sometimes they just go bad.

find out where it's located on his fj and next time it happens have him tap or knock on it with a wrench or something. sometimes it's just contacts sticking. if hitting it makes the fj run, it's got bad contacts and needs replaced. Note: if the contacts are bad enough though, hitting it will not help.

but yeah, it could be many things. but a relay is cheap and easy to replace and i would do it.
best of luck.