Truck stalls while driving?

I have a 1997 Chevy Silverado C1500 with around 210,000 miles and automatic transmission.

This is kind of a long story, so I am trying to explain it as best possible without being too long.

For quite a while I've had this problem of a hard start where I'd crank it and it would seem to crank normally but wouldn't start. After cranking it another one or two additional times it would start and once it started there were no problems. Although sometimes even when it did start it would vibrate for a few seconds before it smoothed out the idle.

Then, and this is the biggest problem, last September I was using it and it totally shut off while driving. It made a sound that is hard to explain that was loud enough that I thought something physically broke, and I was looking underneath it but didn't 't see anything.

I had it taken to a garage who said that there was no spark coming out of the coil and they recommended changing the distributor, which they did.

When I got it back at first it was working but after a short time, like less than 30 miles, it shut off while driving again. I complained to them, and they ended up changing the distributor again saying it possibly was defective.

It seemed to work after they changed the distributor the second time although it still was starting and after a second shutting off but once started it didn't shut off while driving.

I changed the ignition coil and after that got a code that I don't remember what the number was, but it showed Ignition Coil High Voltage.
There is a mechanic who has been trying to diagnose it, but he says he needs it to stall and not start again but it always starts again.

I wouldn't be surprised if it had more than one problem. For one thing he says the fuel pressure is low. Sometimes when on for quite a while it goes down to 40-45 PSI and it's supposed to be 60-66 PSI. But he has got it to stall out by leaving it on for fairly long periods of time but when it stalls it stalls out fast and he doesn't think that would happen from low fuel pressure. He says if it was stalling because of the fuel pressure it would stall more like when you run out of gas; not like if you just turned the key off.

That's the most of it without making it too long. If you want to know anything else, please feel free to ask.