Post up your compression test numbers.
Only then can you tell what the state of the engine is.
If you have not done this, then I am not sure what answers you seek from a forum.
Not sure what truck you have but i believe this is the one.
newera AVR-512.
It needs to be the six wire one.
https://www.newera.co.jp/en/pdf/newera_catalog/voltage_regulators.pdf
sorry, i re-read your post. This is a very interesting problem.
I have never seen a glow plug fail like that, and so uniformly across three of different brands.