(1990 Toyota 4Runner, Automatic, V6, 3L, SR5, 3-VZE)

I have intermittent start problem for a while now and everything in the path of Starting System and Charging system have been checked, cleaned and/or replaced (mostly replaced) based on people’s recommendation on other threads and my own research without results (except I have not touched the distributor yet), but my finding is that it happens more often during the hot season (70 Degree or higher) and long distances (>25 miles)(I have heat shield installed around the starter too). It won’t happen during the winter time as often. I am convinced it has to do with a heat sensitive part!

In this post the only thing I am interested to know is: What heat sensitive parts would prevent car from starting (no click, no crank)? I appreciate it if the answers and comments concentrate on this subject.

Based on what I have researched and read, for example,
Coolant temp sensor may cause rough start but not a no click/no crank start problem. ( just ordered one anyway and will replace this)
The heated Oxygen sensor may cause engine light to come on but it would not stop the car from starting.
Bad thermostat may cause engine temp issues but would not prevent engine from starting.
So, what heat sensitive parts could prevent the car to start (with no click/no crank at all)?

To recap, please note that:

(1990 Toyota 4Runner, Automatic, V6, 3L, SR5, 3-VZE)
1_ It is an intermittent problem and not a hard fail. (it won’t fail when you want it too!)
2_ When it fails to start there is no click or crank!
2_ Even in the summer, as long as the car is running it is fine and temp gauge always reading normally). It is only after a stop and shutting engine off that there is >90% chance the car may not start.
3_ Engine light never come on when this happens and there is never an engine code failure registered.
3_ It always starts after an hour or two of waiting without doing anything

Thanks in advance.