I'll make this brief. Did LS 4.8 swap, engine, trans, harness and all as unit from donor vehicle Into my 91 Silverado. Replaced harness with a unit from affordable efi and had the PCM flashed three different times to ensure it was working (twice by affordable and once by Brandon at LT1 swap). O2 sensors will not switch (move between .450 and .460 mv) truck runs very rich but idles ok. Fuel maps not registering. I have checked the wires going to the front passenger O2 sensor both with the truck running and ignition on engine off. I get 12v for the signal, I have a 12v ground and the heater circuits read .3-4 mv. I have used so many different types of O2 sensors I should go into the business of selling them. I have tried both case and isolate styles with no luck. The plug on the truck harness is square. I have used square and flat O2's (using a harness from square to flat). Any insight would be GREATLY APPRECIATED.