Engine Died then came back to life

[76C10Stepside]

Howdy folks. I've been having one thing after another with my 1989 S10 Tahoe with 4.3/auto. It is in very good condition for a 30 y/o truck, with very low miles (53k), engine very strong.

Couple days ago, the engine shut off while idling at stop lights three times, but started right back up. It has NEVER done this before. It was idling at 750 rpm all 3 times, was running exactly at normal temp, and did not make any weird sounds, etc. When I got to destination a few miles away and was about to shut it off, it died again and would not restart. No smell of gas. Happened to die at a mechanic's house but was going there for a different reason (ironic). He said his Tahoe did the same thing when the fuel pump went out. Engine would not fire with starting fluid (only tried twice). Had it towed home yesterday.

Today, checked for trouble codes, just got the code 12, no error codes. Sprayed starting fluid and it fired right up! Was NOT expecting that.
Idle started at 1250, then 1000, then 750 after about 2 minutes (not at normal temp yet). Ran it for several minutes, ran very smoothly. The only noise was from alternator, but not loud (thinking bearing is on the way out). Checked ammeter and it was dead-center.

I love this truck, but live out in the country, and really need dependable transportation. If I can't get all the bugs worked out of it, will have to move on. Any and all help diagnosing this greatly appreciated!

Here's a history of work (starting with most recent) I've done on it since I got it several years ago. Note that it has sat for about half of that time due to a shorted dimmer switch that took awhile to pinpoint:

1. Just installed new clutch and bearing on the A/C compressor. Bearing was getting noisy and engine was idling up and down. Idle was "better" after this, but still "funny" on some days, fine on others, has had me worried.

2. New MAP sensor (attempt to fix the unstable idle, and occasional misfire). Did not really help.

3. New fuel injector (had already replaced the other one).

4. New valve seals, timing belt, oil and filter change. Later found oil cooler hose clamps were loose, which was causing a slow drip. No more drip.

5. Rebuilt throttle body (including new pressure regulator) and replaced one injector after it started spraying with engine off. It dumped a LOT of gas into the crankcase, had to drain oil and change filter (OK after that, but seems to have cooked the valve seals). Also replaced the fuel filter. The throttle position sensor failed, probably due to my spraying carb cleaner on it while still mounted to throttle body (duh), so got a new one.

6. Replaced dimmer switch (was causing no crank and apparently also shorted out the starter, but not confirmed, as a shop replaced the starter with out my permission, instead of diagnosing and calling me as instructed).

7. Replaced starter (see above). Had replaced starter only 1 year prior too, and had no issues with it.