[F22santiago]

So I went JB4 (map 2) on my 228i (n20) a year ago with no issues whatsoever, love the extra power car pulls strong. A few months ago I also went with AFE catless downpipe. Love the sound and definately feel the extr torque. However, my car now "sputters" a bit when wot on higher gears (i.e: highway pulls). No faults are thrown at all and after 5k rpms or so it clears up. I noticed it seems to happen when its colder so I am assuming it has to do with a fuel and air ratio or maybe overboost (had a similar problem on my turbo saab until i got a dyno tune). So anyone here have any idea what this could be?