I have a similar one. In the late '60s I was an investgator for private company. I travelled all over 6 or 7 western states, sometimes flying, often driving. I had a new Chevrolet station wagon upon which I would usually put 50,000 miles a year and get a new one.

Toward the end of one car it would have extreme problems at first at altitude and then over 50 mph, then 45 mph, and on down. As this got worse I was in Montana and Eastern Idaho. I took the car into shops, got it tuned up several times, and since I was travelling on a schedule I could never take it back to the same place twice. After spending a lot of money, I decided to limp back home and pick up my new car. I wasn't looking forward to 45 mph on a 70 mph freeway.
(Another station wagon. I told my company it was for surveillance, in reality it was to be able to sleep at roadside rest areas.)

I got to a gas station on the outskirts of Boise. An underaged, pimple-faced kid was pumping gas and I casually mentioned the problem. He said if I had 50 cents and five minutes he might be able to take care of it. I didn't want to take the time, but he was so earnest I didn't want to discourage him.

He found and replaced the fuel filter. Solved the entire problem. I didn't know it was solved until I was a ways away from the place, so I didn't tip him, but he earned it.

(I just bought a fuel filter for my car, and now they are mounted on the frame. Bolted in. Kind of a problem to change it without gas running all over one.)

Arf