Just wanted to follow up on this after trying a couple things.
First, I first swapped in some NGK RS7's gapped to 0.024". Here's how they compared to the originals:
View attachment 206080
I've never done plugs before so I have no point of reference for how good or bad the old ones may have been. I wanna say maybe the car ran smoother after the swap but it's hard to rule out placebo effect.
I tried some pulls on Mobil 93 on the Stage 1 91 tune (still v2.50) and everything looked great. I then popped the Stage 1 93 tune (also v2.50) back on. The KR numbers were exactly the same, so we can rule out both bad plugs and Costco 93 as the issue. Maybe it is just lousy winter blend after all. We'll be running the 91 tune for now...