There is some stuff called bluejob and a few other products out there similar that is supposed to work. I would also try bumping all the cells up about 2% or so and see if it helps a little, since you know your exhaust temps are getting high enough to discolor pipes. Also monitor your plugs to make sure they arnt looking like a lean or rich running condition. Another thing is if the TPS isnt calibrated on the PCV software it will lock the throttle reading on the PCV to a cell (mine after just installing was stuck at 100% throttle) You just gotta plug in a comp to PCV hit calibrate and Throttle position, wait for it to warm up then set the value on left for idle by typing it in, crack the throttle quickly and see about where wot's voltage reads then punch that in on Rt side
It is kind of true that single wall pipes stink because if they blue its obvious, with the full heat shield it covers any blueing.