My truck's mileage is low, even for a V10. It stutters at idle, and throws a P0144 code. My exhaust is stock, with a sensor immediately after each manifold, then goes into a Y for a single entry into the cat. There is a sensor before and after the cat, too, for a total of four sensors. I found a damaged piece of harness leading to the very last sensor (post cat) and soldered it back together, and replaced that sensor (in my mind, that was bank 1, sensor 3) and no improvement. What do I look for? I was getting 12 mpg with a tight, new engine, and now, about 6,000 miles later, I'm getting 8 - 9 empty and going easy on it. My local parts shop gave me a universal for the pre-cat sensor; I plan on cutting on the sensor side of the harness so I can save my factory plug and trying that as soon as I can get my concrete slab back.