2000 Subrau Legacy GT Engine Failure

I own a 2000 Subaru Legacy GT Sedan which now has 175000km on it. I've been having an issue with my car since about 93000km, a period that extends over 10 months (I do a lot of commuting). When I'm driving, the engine will suddenly shut off, however, the car still has electrical power to the radio, lights and everywhere else. The Check Engine light is on, and has been on steady for a couple of months now, however, previously, it would stay on for a period of time and then go off for a while. When I try to restart the car, I have to keep turning the key until the Check Engine light appears and stays on, and then I can turn it all the way and the car will generally start. On occasion, when I turn the key to start the car, the Check Engine light will be on, and then go off when I try to start the car, however, all other lights will remain on, but the engine won't start. When I'm finally successful at restarting the car, the 'AT Oil' light is usually flashing and will stay flashing until I stop and restart the car. It seems this issue happens most often after I've been driving, and then stop to go into a store, gas station, etc. And then restart the car. When I try to restart after stopping the car, the Check Engine light often won't be on the first time I try to turn it over, and after a few attempts at turning the key part way, the light will come on and I can start the engine. During my work week when I get in the car and drive the 140km to work and then back again at night, the problem doesn't occur as often, and sometimes not at all. When I have my days off and I'm doing some running around town, stopping and starting the car constantly, this problem occurs non-stop.

I've had the car into the garage several times and spent over $2000 on a variety of repairs and obviously nothing works and I'm ready to drive the car into a tree. So far, they've replaced the transmission fluid, battery, tires, ground wires, fuel filter, gas cap and nothing has made a difference. All of these repairs seemed suspicious to me, but I took the Subaru mechanic's word for it. Now I obviously have no trust whatsoever for the Subaru dealer's mechanics. I've asked them to check the fuel pump, but they keep saying that couldn't possibly be the problem, but to me, it seems like a logical thing to at least test.

Can you shed any light at all on this issue so I can go into a reputable mechanic with some sort of direction?