Reverse is slipping

change oil

The only way to rectify this is to remove the tranmsission from the car and tear it down for repair.

The high viscosity ensures transfer of lubricant throughout the gear train. Some modern automatic trans-axles (integrated transmission and differential) do not use a heavy oil at all, but lubricate with the lower viscosity hydraulic fluid, which is available within the automatic transmission.

I have the same vehicle, with the same issue. I had put the car on a rack and lifted it to pin point the cause of the clunk when shifting from park to reverse or reverse to drive. I found that the front diff mounts were grenaded, meaning they needed to be replace bad. with these mounts being bad it was causing the front diff housing to slam the frame up and down when shifting from park or reverse to drive. this is pretty expensive to fix, your talking $160 in parts and $540 in labor. I also had the service 4WD warning display on my dash cluster, i had the code read. It came up as a bad solenoid in the rear diff. this is about $200 parts and labor to fix. Also, dont know how many miles are on your jeep but if you've ever sub-merged your axles under water or if your over 60,000 miles you need to replace your gear oil in the front diff, rear diff and transfer case. This is a little costly to have a mechanic do as well because you're supposed to use synthetic gear oil. For a shop to do it you're looking at $360.

i have the same problem 2005 xterra 4x2 giving pretty much all the code you posted but i did and tried everything possible to fix it myself with a little success but still ( Engine Light ) comes on with the last code P1757 front breake soleniod i did change the front passenger sensor but now the light came on again i believe the driver side need to replace as well ..... but weird the whining noise from the engine still there sound like i am going 120mph but actually im going 30mph only initiall problem was fixed by replacing the Transmission Oil 5 qrt S type from nissan dealer it did help for at least few months but then the problem came back... i also replace the Transmission Revolution speed sensor by doing that id just eliminate the code to pop up... i love my xterra but im getting really fraustrated everytime i see her in my garage colleccting dust not running.. dont want to spent a fortune rather thingking about trading it anyway like id said you might thingking replacing the Transmission oil that would maybe solve the issue.... GOOD LUCK....

Will it move if you put the transfer case in low range? If so the there's a good chance the reverse clutch is going out. Did it go all at once or did you notice some slipage? If it went all at once it could be a hydraulic problem or broken internal parts. It takes more pressure to apply reverse than the forward gears so it could a valve body or pump problem. Is it full of fluid, is the fluid dirty (brown or black)? I think Ford recommends changing the fluid at 30,000-50,000 miles change the transfer case oil too.

When was the last time you shifted to 4WD?

If you do not use 4wd too often then try this old trick.

Next time you're going off road try to do the shift to 4WD,shift to reverse and drive in reverse for 6-12 feet.
(no gas //1 mph //SLOWLY)

Driving backward for few feet help the gear pickup the lubrication and let the gear sync up better.

Check your Xterra gearbox lube schedule.

Sounds like a bent fork in the transfer case. It is a common problem with your truck. The transfer case is a np236. If it just recently started doing this, the rebuild will cost around $800. If the 4wd has been acting up for a while, the planetary will probably need changed, which is another $200.

If you have an owners manual, look in there it will show you what needs to be done.
Change plugs
Change air filter
oil change
change all fluids
Transmission
coolant
check brake fluid
check hoses, wires, etc.

I have a 2005 Tahoe that recently had a similar problem. To resolve, I did the following.

1. Change the transfer case fluid (Which you already did)
2. Change Gears to 4L while in neutral, change back to drive, and drive slowly 50 yards or so.
3. Change Gears to 4H while in neutral, change back to drive, and drive slowly 50 yards or so.
4. Change Gears to 2H while in neutral, change back to drive, and drive normally for a couple of miles.

This will cycle the fluid within your transfer case, and hopefully clean out the sensor. I did this, and my Service 4WD light went away after one day of normal driving. Hope this helps. Note: When I went into 4L the first go around, it had a hard time shifting due to non use. I changed between 4H and 4L a few times until it got smoother.