I just replaced all 4 and thought I would share what worked best for me.

I have 2" lift, so I am able to get under my truck with a creeper and still have room. For those that dont have a lift, jack up the front with either ramps or jack stands. I also used a O2 socket from Harbour Freight that was $7.

The rear O2's are pretty straight forward and easily accessible. Make sure you run the new O2's the same way as the old ones. The O2 on the driver's side runs through the frame / body mount. The O2 on the passenger side gets tied on to the wire harness. If you don't tie it, it may get tangled in the front driveshaft.

The passenger side front O2 was easily accessible from the top of the engine bay. I removed 1 hose from the SAI and was able to unhook the old O2 from the top. I used a bunch of extensions (about 2-3 feet worth) and removed the O2 from the engine bay. Install was the same process reversed. Everything for the passenger side front was done from the engine bay.

The hardest one to replace is the driver's side. For this one, I had to un-plug it from the bottom. You can pretty much only get 1 hand up there at a time. I found that removing the whole plug from the holder first was the best way. I used the same extension set from the engine bay to remove and replace the O2. Back under the truck, I plugged it in and put it back on the holder.

I did not pre-heat the truck because of the close proximity of my arm and the exhaust. Spraying some WD-40, PB Blast, etc on the O2 sensors worked just fine and with the socket extensions, I was able to use a breaker bar no problem. I have 110K on the clock and my exhaust is always covered in red clay (I live in NC) and the O2's came off no problem.

All said, it took less than 1 hour and wasn't too difficult at all.