I breezed over all the posts and i didnt see anyone mention or ask what octane rating you use. I saw that you mentioned you use premium gas, did you mean top teir gas or high octane gas? Because high octane requires more energy to ignite and although it idles fine, that initial spark flash may not be up to ***** to fully ignite for an even burn. Uneven burning would put stress on a piston on its way down for the powerstroke.
Imagine someone getting a clean right hook to the head in slow motion, the head moves and the face has to catch up. Thats the best way i can describe it anyway
Well cars can now detect knock etc more efficiently now and can adjust spark timing for it.
This is where i believe your hiccup is occuring, the time between the first uneven burn and the adjustment of the spark timing. If the uneven burning is corrected once the engine finds its rhythm it will adjust back for efficiency and you wont even notice. Otherwise i believe it would throw a code
I maybe way off but if the fix is as simple as filling up with midgrade, while its cold out i would give it a shot.
high octane is the cause of many problems for people. They hear it burns hotter and it cleans the carbon and makes the engine run better etc. high octane is designed FOR high performance engines, it dosnt MAKE an engine high performance.