16 Mustang GT Auto. slight hesitation at cruise rpm. HELP!

[STLSinger]

Mods - Stainless Works full lenths 1 7/8 no cats to 3" collectors into corsa extreme catback

after in stalling the headers i noticed a slight miss while cruising 1500-1900rpms any gear. removed the ac line bolt i thought was causing a false knock. also checked the imrc connections and lines (they seem ok but not 100 percent sure) weve tried going back with the stock airbox, no help. and a tune revision (almost seems worse).

stock tune runs alot cleaner but throws catalyst codes. i think there is still a miss but barely noticable. when i load tunes in it makes the problem jump out for sure. my tuner guy says the logs look ok.

would a vacuum leak show up on a log or a faulty imrc or if its sticking?
i did change the plugs and swap the #8 coil pack with another cylinder (i was getting a p0300 and p0308 code which im not anymore)

where should i start to diagnose the car since i think its a mechanical issue?

[Jn2]

Post your tune and a datalog where the hesitation occurred. If you are not the one tuning it then refer to your tuner....