Motorcraft doesn't make the upstream o2 sensor for my 2006 mustang gt anymore but says the downstream o2 sensor will work. I've replaced the o2 sensor with three different Motorcraft part #dy-1401 and I get the code that says slow response from that o2 sensor evertime. Switch it with the other side that has the original one in it and it works. Anyone else have this problem since ford decided to do away with the upstream o2 sensor?