Another GC8 exhaust opinion thread - opinions wanted

[ZiN]

Just an update.

I got the Hitech installed sounds and looks great, very happy. However resonator is only 7cm of the floor, although the stock exhaust would rub occasionally, car is quite low.

It was running rich but got the best fuel economy ever 9.9L/100, probably because I was trying to be careful while untuned. I got a tune for the exhaust just to smooth out the rev range and avoid any future issues, got an extra 15kw ATW too

However after the tune I've been having Idle rev hunting, sometimes getting close to stalling. I replaced the O2 sensor because tuner said issue went away while it was unplugged. Issue is a bit better now but still occurring and I'm still trying to locate the cause, my idle was pretty smooth before the tune but I'm told it's not the tune.