2001 Chevy Silverado Turns over, won't start

Truck stalled out at a stop light and won't fire back up. It has new plugs, wires, rotor. I assumed it was the fuel pump as it was not holding pressure in the lines. I replaced the fuel pump, and fuel pressure regulator. Now has plenty of fuel pressure in the line, and plenty of spark. Turns over but will not fire. Code says fuel mixture thin in right and left bank oxygen sensor, though I don't think the O2 sensors would prevent it from starting. I think the codes were left from when it stalled out.