Intermittent stalling and loss of power?

Hello, did your mechanic drain the entire tank? Bad gas can cause so many issues, it can actually ruin fuel injectors. I have also seen bad gas cause ignition coils to fail multiple times in a row. But since this only happens intermittently, you can try putting some dry gas in your tank in case there is any water at the bottom, and it is occasionally drawn up into the fuel pump. Also, some fuel system treatment can help. It depends on what was in the bad gas you got. Sometimes there is water, sometimes there is alcohol if the gas station had the wrong type of gas put in the wrong unground storage tank. Techron is a great fuel treatment to add.
Is this happening at any certain fuel tank level? Such as a quarter tank where it would be more prone to pick up whatever might be left in the bottom of the tank.

Looking through service information, this is a direct injection fuel system and they run at extremely high fuel pressures, so having a shop go over some live scan tool data could help. There are two fuel pumps in this system, a low side one in the tank and a high-pressure pump that is driven off the camshaft and can run up to 2,000 PSI. It's not a system you will be able to work on yourself. They are also very prone to carbon build up on the intake valves because of the direct injection into the cylinders and they need intake valve cleanings. That might be causing your issues.

I think it might be a combination of things, water, moisture or alcohol in the gas, they tend to settle at different levels in the tank. The water is heavier than gas, so it goes to the bottom of the tank. A couple of cans of dry gas, one with each fill up will help get rid of the water issue, just follow the recommendations on the container, The intake valve cleaning is actually a walnut blast. I know the name sounds strange but that's what it used. The intake manifold is removed, and the machine is hooked up to the two ports and blasts the valves with small pieces of walnut. It works amazingly. Because the fuel injectors are no longer located in the intake manifold and behind the intake valves, and the fuel injectors are actually in the cylinder, the gas being sprayed in by the older style system would normally help to clean the intake valves, but that is not happening now. Below is an example of what happens to valves on direct injection engines. This carbon build up also ends up on the tips on the fuel injections just making the situation worse, so if it has never been done on this vehicle it really should be.
The valve cleaning is recommended between every 22 to 44,000 miles. So really it should be part of a normal 30k service. I don't think it's the Fuel Rail pressure sensor. You're correct, you would have a check engine light on, and most likely the vehicle would be in Limp Mode with reduced power.
A fuel system cleaner will help to clear up the fuel injector tips but Google direct injection intake valve cleaning for some more information on it, this will give you a better idea of why it needs to be done.
The engine computer will eventually start to flag cylinder misfire codes, it's probably not doing it yet because the issue is coming and going.
here is a video of the process as well, he explains how it is done and what happens when it is not done pretty well. Hopefully this will clear up the issues you're having. I fully understand how frustrating a tank of bad gas can be, I spent a full week repairing a Jeep that had a full tank of extremely bad gas. It actually caused an ignition coil to get hot, short out and ruined the engine computer. So, I recommend getting gas at the same station where you know the gas supply is fresh each time, at least in your area, obviously you can't do that if you go on vacation.
But let us know how you make out, and if you have any more questions.

https://www.youtube.com/watch?v=KFvXbTIiAVY