2001 Hyundai Accent loses power or stalls

My Mom's 2001 Hyndai Accent with almost 40,000 miles started losing power and quietly dying while making a turn or on the road after attempting acceleration. Then it starts up again OK and runs. We have taken the car to two different well-recommended mechanics, and they have had diagnostics run. The problem doesn't always happen, so it's hard to diagnose, and when she gets the car back everyone thinks it is fixed, and it does the same thing after she drives it for a couple of days. The car has had sensors changed, computer changed (replaced with used one), transmission changed (with used one), more sensors changed, new fuel pump. And this morning when she was driving, the car did the exact same thing, quietly stalled in traffic, but then it starts up OK and runs. Also there is a problem with not being able to pump gas but a trickle before the gas pump shuts off. I always pump the gas for my Mom as she has a hard time removing the gas cap. Before this stalling problem started, the gas pumping problem went from bad to worse, where I had to pull the pump handle partially out to allow air in and allowing in just a trickle of gas, so the gas would not cut off. Is there any possibility that the problems could be related, that there could be a problem with the gas flowing to the engine if the fuel breather tube is completely blocked. And when you turn the engine off, sometimes it there is a quiet tic-tic-tic-tic sound, which sounds like it is coming down the exhaust pipe.