I drive a 2016 WRX 2.0L MT with Invidia turbo back catted exhaust and Cobb cold air intake on the Cobb stage 2+bigSF tune running 91 oct. fuel the best I can get in Utah. I've been running this tune for 20k miles and do oil changes every 3K miles. Last week I left my house to drive to work and I noticed when giving the vehicle around 40%~ or more throttle at 3k-4k RPM the vehicle will hesitate throughout that RPM range and after 4k-4.2k RPM the vehicle drives normally pulling full boost and is putting the power down as normal. What I've noticed while watching my boost and AFR at 100% throttle, the boost will be relatively normal but the AFR will go from 10.80 - 14.10, when normally while at 100% throttle the AFR is 10.14 - 10.90. I'm not sure what is going on but I have ordered a new air filter but it has not arrived yet, the spark plugs are NGK laser Iridium and only have 15K miles on them, I have never changed the coil packs while I've owned the vehicle but from what I can tell it doesn't seem like a spark issue. I'm more leaning towards fuel or air flow issue. If you need more info tell me what you need and I'll answer to the best of my ability! Thanks in advance.