The symptoms you are describing, almost bet its fan related.
Had nearly same issue with mine several years ago. Had a cheap, parts store fan on it and would heat up quickly on the street or the track.
Bought a GOOD fan, immediately fixed the issue.
By good, if a fan isn't pulling 20 amps or better, its motor isn't cutting the mustard. I have found Derale fans to be of excellent quality, and they are US made.
Having them on a relay(s) is also a good idea
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, 10.40 @127 1/4
1.41 best 60 foot
6.60 at 103.90 1/8
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