90 740 GLE random stalls then no start (for 20min)

[Maui740gle]

My ex drives our kid around Maui in a 1990 740 GLE (non turbo) (B234F w/ Bosch ignition) and it's been stalling at the most inconvenient (and dangerous!) places and not starting for say, 20-30 minutes (then it seems to run fine, at least for another 15-20min. Our savant mechanic with an inherent drive to sleuth out problems is stumped as to why this intermittent stalling is going on. This seems to be happening when it is warmed up, first did it the after "acting funny" in 4th of July bumper to bumper traffic over in Lahaina, when it got to it's destination, it crapped out in the driveway.

Then, it stalled coming home the next day (fortunately right by beach park), a hot day, so I went out to get here a tow. Got rope on, it starts. Take rope off, realize I killed my battery in my Subie Outback while I was fiddling around with the 740, so she pulls it around to jump the Subaru, and it craps out again. So, we get someone else to jump Subie, I turn around to tow her and we go about a mile, tow rope snaps after crest of hill, but, 740 starts up and makes it back to Pa'ia (about 12 miles from that point).

Next day, mechanic looks at it, starts fine. No problem is reproduced, so hard to diagnose. Tonight, it stalled out again and started right back up a couple times during the day, then really stalled out turning onto the busy Hana Hwy from Baldwin Beach, thought I was going to tow her again, but 20 min later, it starts back up. So, for the second night in a row, I follow her home, but tonight it stalls out when making tight turn uphill to get to her neighborhood. So, I manage to tow her up and over to her place. (Accidentally took off front bumper when hook slipped, but I got it back on). And, of course, it starts right up.

Some background:
-fuel pump relay has been tested and is working.
-fuel injector relay was checked awhile back (had to be rewired after it came loose)
-a couple weeks ago two of the injectors were replaced (or fixed, not sure) after we thought it was really going south (oil in plug cylinder, power loss).
-spark plugs replaced at same time injector issue was being assessed.
-fuel pump and filter underneath were replaced last year. (could it be other fuel pump inside tank?)

This is driving me nuts! Every time I turn around this thing is stalling! Help!

[lummert]

Weak or non-working in-tank pump combined with high temperature and low fuel level can cause this type of problem. Make certain that the in-tank pump is operating. Also keep plenty of fuel in the tank.

[JerryC]

As lummert said. But also, change the power stage. These are a frequent source of random no starts. CPS is also possible.
"fuel injector relay was checked awhile back (had to be rewired after it came loose) "
If you mean the radio suppression relay which is the fuel injection relay, a black box with a square connector with 4 wires, 2 large and 2 small, these also are a frequent problem. What does "was checked" mean exactly? inspected all board solder with a magnifying loupe? Some have success with reflowing the solder, but I change them.