First rule of PETG-club is "dry your filament", second rule of PETG-club is "dry your filament"... Thrid rule? Nope, it's "store your filament dry"
Jokes aside, other things you could look at:
- nozzle, how worn is it?
- calibration tests: did you do a temp tower? Calibration cube? Retraction test?
- The vertical surface doesn't necessarily have that appearance as a result of wet filament. In my experience, wet PETG will result in more random variations than that. It looks too regular IMHO, is everything that should be tightened actually tightened?
- have you calibrated the extruder steps?