Hi all. I'm hoping someone can enlighten me with an issue I'm experiencing. It is easily repeatable on the highway and only seems to occur in 6th gear at WOT or near-WOT. If it wasn't for the lack of a flashing CEL and the fact it doesn't feel as "aggressive", I'd suspect a misfire, but you can really hear the turbo sputtering and there are "bumps" in power when it happens, if that makes any sense - almost as if the turbo is cutting off for fractions of a second over and over until you let off the gas/decrease the aggressiveness of the acceleration. In any other gear, it pulls strong and smooth without issue. The issue is noticeable enough to where my wife (who is by no means a car person) can detect the sensation and inquire as to what's happening.
I've tried searching for similar issues but I can't seem to pinpoint the answer, or even someone who describes this exact problem. I realize it's generally not advisable to floor it in 6th, but I'm talking speeds of 75+ and considerable RPM (3K+), so I don't suspect it should be different than flooring it in any other gear at safe/appropriate engine speeds.
Could this be, in fact, a spark plug/coilpack issue, or more likely a turbo issue, given the description? I'd be happy to provide further details - not sure if I'm covering everything. Thanks to anyone who chimes in; maybe this post can help someone with the same issue.
The car is a 2016 6-speed manual with an aftermarket Sachs clutch kit, running APR's Stage 1 high-torque tune (I believe) - if that's of any interest.