99 Ranger 2WD 3.0 V6 Flex throwing code P0133, and my friendly mechanic with the computer wrote down "HO2S11 Circuit slow response" [his '5's' and 'S's' look kinda the same, or am I writing with a lisp?]. I'm told it's bank 1, sensor 1. I recently replaced the DPFE which was throwing a code, and now I have only the one code to solve. I have a new air filter, no exhaust leaks, and everything looks good otherwise. It seems like I've covered the obvious bases. I'm thinking my next step is to go after the sensor and use genuine Motorcraft because I've seen reports of aftermarket brands not holding up. Other thoughts? Advise to save my knuckles?