Darn, I got into this too late and you solved the basic problem. (Lift the radiator cap and drive a new car under it).

I wanted to reminisce. In the 1950s I had a car that died at stop signs. Everything was fine until everything would just go dead - even headlights and dash. I would look at it and wiggle everything and it would start.

Finally one night I pulled forward on battery terminal and the lights came on. I hammered a nail in the battery in the proper place to tighten it forward and all was fine.

On another occasion a friend of my brother was stuck with his new car not starting. I took my volt/ohm meter along and battery was fine. So I took resistance readings on terminals to see if it obviously needed cleaning - nope. Finally I tried to read across the cable end to cable where it was a clamp on end. Bingo no reading. We unbolted the cable end and it was really corroded in there.

I was betting you had a dirty cable where it clamps to the end piece. But then you did not say if it was side terminals. They can get corroded inside and you need to unbolt the cable and pry the rubber cable-end-cover off to even see the corrosion.

Go find your old truck and check it out with a volt-ohm-meter just for laughs.