My own experience with memtest86 and memtest+ is that I have never seen false positives. Plenty of false negatives, since they do not catch every problem; they cannot prove hardware is good; they only help identify bad hardware.
I've never had heat problems during the running of these tests. If I wanted to test power supplies and heat management, I'd run stress testers instead.
You are more likely to have a memory problem than a heat problem, based upon your results..... of course, a heat problem could manifest as a memory problem.
