This thing looks like a bear to get to and remove. Ive seen some 3rd and 4th gen threads, but no 5th. Nothing on Youtube either. Anyone done this before?

I've changed 3 on my Tundra. Pretty easy if you have an O2 sensor socket. It has a cutout to accommodate the wires. Spraying a little penetrant makes removal easier. Make sure the replacement has the connector - some require you to splice the wires. I use a little anti-seize on the threads to make eventual removal easier. I have heard you can extend the life of your sensor by removing it and using a torch to heat the end and burn away the residue that may be causing the fault. I haven't tried this though. I have just used a code reader to erase the code and it works for a while. I have one now that's acting up. I erased the code a couple of months ago and it hasn't come back yet. However, I don't drive that much now being retired. As far as clearance goes - you might have to get creative and try a 6pt box wrench or something.

Thanks. Did do it completely from the bottom?

Yes, I did all mine from below; after letting things cool off, much more room. On the Tundra I didn't have to raise the vehicle. My 2013 4Runner is a little closer to the ground; so I would probably raise it up some. Also, be kind to the connector - it's probably dirty and might not want to come apart easily.

Did you ever successfully get your upstream o2 sensors out? I have a 2011 and they seem impossible to remove without some serious part removal. I cant figure it out. TIA

Mike