Thanks for all the input folks. I can't say it enough.

I disassembled and cleaned everything between the airbox and the throttle body, cleaned the MAF, new air filter, and reconnected the battery on Monday. Done that exact process at least three times in the last two months.

(Been through three air filters this winter on account of how sh!tty and dirty the paved roads are, not to mention the gravel. Also these Nokion tires are THE BEST STUDDED TIRE EVER MADE but they throw a lot of sand/rocks. The most recent filter was only a month old, but I had a new one on hand, so I swapped it.)

I let it sit for a day and drove back into town today. No codes so far. Spent $200 on a Innova 3100 at my local NAPA, hooked it up, ran errands around town and drove home. Still no codes. ~40 miles total, hills, highway, gravel, 4WD, same as always. Since this problem cropped up, the Check Engine light has always come back on before I complete the trip, within 20 miles. Not today Satan!

LTFT at cold idle was -5%, -3.9% at warm idle. 0% around 1900rpm and 60mph. It never exceeded the range between -5% and 3%.

MAF was right around 0.5 lb/min at idle.

All other values seemed within range... and that fuel trim fluctuation seems pretty darn minimal.

...so I guess I'll be up here, waiting for something to fail again.