I live in a western state as well. And just today got a certified letter from the EPA say the EXACT SAME thing !! My state limit is 20 %. All i do is put my stock plate back in, stock position. Put the AFC back and go in with gauges, big turbo, and bolt my cat back in. NEVER question me. Only thing is that its one of neighbors turning me in and i dont even smoke my truck unless im racin or hot roddin. which isnt very often. Thing is i just passed emissions and im pursuing this further. its bull that some joe blow can just call and complain, and i HAVE to my truck down on MY time, MY expense, just to be legal !

 

I bet you can bribe one of the other nieghbors to find out who got you pinched. Then call in their license plate two or three times.

 

my 08 6.7 engine is completely stock.
but my '83' 2.2L (non-turbo) diesel ranger, smokes anytime i step on the throttle. going up any hill leaves a nice trail.
i drove the truck into the l.a. area a couple years ago. you should of seen all the rude looks and yelling out of thier windows at me. the truck is pretty much stock. but to keep the smoke down i do mix veg oil in the diesel.