I GAVE UP. I mean, this little sucker was just too tough to budge. I knew it'd be hard to remove it so I soaked with penetrating oil for the past two days before I worked on it. I warmed up my truck for 2 minutes ( well, probably not long enough, now that I think about it, consider it's -5 out). I bought a 7/8 O2 sensor removal socket for the job. When I slid the socket on with my 3/8" impact ratchet, the ratchet wouldnt even move. I obviously couldn't use the 1/2 impact gun as there wasn't enough room for that. So I am here looking for help. How to remove upstream O2 sensor? Any help is greatly appreciated.