1990 Legacy random power loss (died while driving) gremlins!!

[CharlieLS]

Hi all!  I'm back with New Problems!

First off, thanks again to everyone who has helped me before.  I love this forum for the wealth of knowledge and helpfulness here.  I have searched extensively and read a bunch of topics from years prior that seem to relate to this issue, but I'm stumped on solutions!

My 90 Legacy (2.2L LS AWD wagon MT), which has been a total trooper with very few major problems given its age, recently (within the last month) has sporadically (VERY sporadically) been acting "weird" (random bouts of sluggishness like it's not getting enough gas or something, lasting only a few minutes and then seeming normal) and randomly died in traffic a couple days ago. It wasn't a "chug chug die" like running out of gas or even alternator/battery death.  It was just a silent power-down, Do Not Pass Go, we're done here sort of thing.  Also, all the cab electrical stuff and the power seatbelt and door locks were still working fine. I was able to fire it up again after a few tries and panic-drive it onto a side street where it "powered down" again and would not restart.  I grabbed some new gas from the gas station just in case it had anything to do with that (I was low on gas but not critically low - my gas gauge is intermittent but I always set the trip meter and have done so for years, so I know I wasn't - or SHOULDN'T have been - anywhere close to running out).  Dumped in a gallon of gas, got the car to restart, drove it to the mechanic about three blocks away, they did some (cursory) diagnosis and couldn't find anything electrically wrong in the engine compartment.  Drove it home, and just kept feeling that weird sluggishness like I wasn't getting enough (mechanical) power, but there was no (electrical) power loss, and it's been starting OK since (with caveats, will describe below).  I'm just nervous to drive it if we're gonna do this mysterious-will-I-won't-I dance at random times. 

Here's my summary so far of what has been done recently and what has been looked at in this instance:

Mechanic checked:

Engine compartment wiring and grounds - said everything looked OK
Alternator (which is new as of 2 months ago) - said output is great
Battery (2 years old) - checks out fine.
They also could not replicate the problem, but admittedly didn't do any highway testing or even very much driving beyond taking it around the block a few times.

I never got a CEL when it died, but I checked for "hidden" codes anyway, and got:

13 - camshaft sensor
14 - crankshaft sensor
and uh....4. Which doesn't appear to exist as a code.  😆

Started up for me OK this morning, with a little bit of hesitation to turn over which is fairly usual for me in cold weather when it hasn't run in a couple days.  From reading previous posts about related issues, I tried:

Thumping the MAF with a screwdriver to see if I could get it to stumble (Nope.)
Checking the coil pack/coil pack wiring to see if there was any looseness/cracking (Nope)
Wiggling/disturbing various parts of the wiring harness, mostly the camshaft and crankshaft sensor wiring to see if that caused any change (Nope)
Checking all engine grounds for tightness/cleaning, etc - all looked OK and that had been confirmed by the mechanic a couple days ago anyway.

Stuff that has recently been done on the car:

- New alternator as mentioned
- crankshaft sensor replaced last year, this is the first since then I'm seeing a code for it
- camshaft sensor replaced twice within last year:
first replacement due to recurring code, plug and play replacement by me, then when it coded again later due to mice chewing on the wiring, the harness was "repaired" by a shop.  They hardwired it in, so when that sensor threw a code again six months later after timing belt replacement, I had to cut apart their wiring to replace it again.  Not gonna say my wiring is the best, but I can't seem to get it to fault or cut out by wiggling it so idk? I'm very stupid when it comes to electrical though.
- timing belt replacement six months ago due to the belt I bought and replaced a year previous breaking.  New belt is a straight Subaru replacement part rather than aftermarket.  Rollers/bearings replaced too.  These were all double-checked in September when we had the engine block out for head gasket replacement, and they all move freely and smoothly.
- fuel pump replaced last year
- fuel filter replaced two years ago
- spark plugs replaced in September
Not strictly related, but
- head gaskets/valve cover gaskets replaced back in September.  (mentioned because having the engine block out did give us a chance to look at wiring and nothing jumped out as problematic)

The only other things I can think to mention at the moment:
- I do notice a much more significantly "gassy" smell when first starting the car than there should be, maybe?
- I replaced the fuel pump relay earlier this year just because I was swapping out the HVAC/heater relay but it's not what one would call "new." (grabbed it from the junkyard)
- clicking sound from under driver's side dash when I turn the ignition to "ACC." Would this be the fuel pump being primed?  It's a slow click, and continues as long as I have the key to "ACC" (with none of the diagnostic circuits connected so not like when you have the green ones hooked up and it's the fan relay or something)
- not sure how this would be related, but after the alternator replacement, my radioset digital display won't stay on with the unit powered off (aka, just showing the clock).  I have to keep hitting the "DISP" button and after hitting it about 20 times it will sometimes stay on until I turn off the car, sometimes won't.  Probably just old/something got messed up when the alternator died? Anyway, again, pretty sure that's not relevant to this.

Anyway, thanks for reading and hope someone has some insight!  This car is my only vehicle so it's a big bummer not to feel like I have reliable transportation this time of year, for sure...
Hope everyone's having a great day!