The guy did this three years ago...
Aside from that...
The fix is to set the codes to "No Error Reported" or switch the O2s off in the tune. Rear O2s have no effect on driveability. They only measure for converter function. High flow cats will not be as efficient as OEM cats and therefore will set the code. It does not effect the engine or how the car drives.
I agree with the above statements based on my same experiences. I believe my latest tunes have the rear 02 sensors turned off.
2013 GT, Track Pack
, Recaros, Kooks Axlebacks, Airaid CAI, BMR Rear Adj. LCAs, BMR Relocation Brackets
, JLT Oil Separator(s), Barton 2 Post Shifter Bracket
, Steeda Motor Mounts
, Barton Shifter
, JHR Clutch line, BMR adj. UCA and Mount, Kooks 1 3/4 headers/catted H, DSS Al Shaft
, BMR Loop
, Vogtland Sport Springs front/BMR rear, Strange Adj. Struts/Shocks, Extended ball joints, Steeda Bumpsteer Kit, Whiteline Tranny Mount Bushing, Borla Overaxles, BMR Watts, Vorshlag 3" Ducts