F250 6.2 Strange Idle Stumble

[Bill-2020]

To the F250 6.2 gasser owners... I have a 2020 (6K miles) that has a strange "idle stumble" in the warm-up cycle (about 1/2 the way into the warming time), and then the same "idle stumble" after warming up, but not as pronounced as when it's warming up and beginning to idle down a bit. The stumble is like it almost has a misfire, but no codes are thrown. It doesn't do it so bad where it would seem as if it's trying to stall or anything, just as if its lost its timing or something for a split second. This was first noticed at about 1500 miles, but I had not stood by the side of the open engine bay during a warmup cycle or let it idle in park/neutral yet.

My idle sits just above the 500 RPM line on the dash (Low 600's according to the scan tool in live mode) while in park or neutral, no load. It idles smooth and then the "stumble happens for a second and then it's gone... then it comes back. Very repeatable without having to try.

If I'm in Drive, idle speed remains the same and the "stumble" is nearly gone. Also, no A/C on, no other heavy loads on the engine when this happens. Driving? Doesn't seem to do this at all. But it's subtle enough that at idle, I can feel it in the seat as the body of the truck wiggles just a bit, so when driving I'd never be able to tell the difference between rough road and idle stumble. When it happens the idle needle sometimes moves down ever so slightly then back up to where it was, but it's very slight.

I've changed fuel from non-tiered to top-tier gas, no change. I thought maybe I got some bad fuel so I dropped in a couple cans of Seafoam on a fill up recently and burned the tank down to empty with no changes. I tried a mid-grade octane tank of gas, no change either. I'm used to a smoother idle in a large V8. (Tundra 5.7, in know apples/oranges, but still...).

Is this a normal thing for this particular engine? I've checked for vacuum leaks, I hear nothing. I've scoured the web and multiple other Ford forums and what I find is those who complain about this have 10s of thousands of miles on them and a tune-up corrects the problem. But their idle problems are much, much worse than mine.

Ideas? Experience with this? A trip to the dealer for insight is next, but I wanted some opinions or knowledge of experience on this before heading to a dealer. My brother's 2020 doesn't exhibit the same stumble, for what its worth, but then again he's at altitude so things may be different.

(this 2020 6.2 engine is slightly different than previous years. The air filter is actually the same size and same air box as the 6.7 diesel, but no gauge on it and no prefilter. The mass air flow (MAF) is behind the throttle body instead of between the air box and the throttle body. Those are the only changes I've been able to see so far.)