IMO, even the early Volvo/Chrysler Ignition system is perhaps the most reliable thing under the hood. I think your intermittent power loss and running hot could be due a catalytic converter problem, rather than anything in the ignition.

We had an '87 240 whose cat converter "guts" came loose and, with time and vibration, the debris formed a compact ball of scrap about 2.5" in diameter (discovered during autopsy).

Under varying conditions of acceleration and terrain, this "cat ball" would roll back and plug the cat outlet, producing much the same symptoms as you describe.

When the car stopped (or sometimes under braking decceleration), the ball rolled forward freeing the exhaust, and all was well till the next time.

It was really a solid problem, only the conditions causing it were intermittent. Try pounding the bottom of the cat with a rubber mallet or the heel of your hand, and listen for anything rattling inside.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.