Try using a different brand of fuel with higher octane. Don't use any gasline antifreeze or other additives in that tank. Sounds like severe detonation going on inside. If it persists get it in for a timing check or see how much carbon is on the head/piston causing higher compression and retaining heat. let us know what you find. Had something similar happen to me here a few years ago. Turned out SuperStore uses BARRELS of methol alcohol in their winter gas for our -40 temps. Check your plugs when it happens for color
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