1996 Other Oldsmobile Models Stalling while driving!

Here's one for you:

I have an Olds 88 with a 3.8 v6. I've had it for roughly six months, but the last three months have been spent attempting to figure out why it stalls randomly. The first time it had done it, I was in a parking lot. The engine just stopped. No sputtering, no nothing. All the dash lights came on. Took a couple of tries to get it to restart, and then it ran fine the rest of the day. Afterwards, it usually does it while it's in motion or if I'm at a light and go to accelerate. The engine just cuts off just as quiet as can be, though I do realize that right before it does this and I'm pressing the gas pedal, it acts like I'm just letting it idle-- as if it weren't getting gas).

No engine light comes on and no codes come up for my mechanic. It's stalled when it's cold, faster when it's warmer (but not all the time). We had run a fuel system cleaner through it once and it ran perfectly fine for about a month until the first warm day we'd had. The only time the mechanic ever got it to stall is when they were pulling it into the garage and tried to roll the power window down-- Started up, tried the window, and it happened again! He took it out for a drive and finally, somehow, got the engine light to come on. Code for random misfire came up, replaced some rather lousy plugs and wires. Car ran beautifully-- until about three days later. I was pulling out of a parking lot and it stalled. It didn't take much to start it back up, but I realized that the windows didn't work when the key was turned on. When they finally did, the car started right away.

I don't have a terrible amount of cash for guessing games, and I understand that this sort of situation is so hard to pinpoint, but I'd like to see what you think. The fuel pump is about running about 5lbs low on pressure, but it works (mind you, I don't hear it kick on when it stalls and I try to start it, which may have something to do with the power window business) and no one seems to think it's that. We've talked about the ignition module, but the voltage and such comes up fine. We've actually cleaned the EGR valve and it runs perfectly.

So frustrated! Please let me know what you think! Thanks!