I would be working on my own "second opinion" before selling the truck for 4k.
Rear diff is a known failure point, sure, but I would look at the parking brakes to make sure the noise from the back wasn't the brake shoes delaminating. If the brakes failed and took out the axles, then I could see the dealer not wanting to replace parts - they seem to like to replace the entire rear axle as an assembly. Quicker for them, expensive for you.
I'm really skeptical that the transfer case would be bad, unless it was already damaged, coincidental to the rest of the story. Same for the front diff. Perhaps the Nissan shop was a bit overzealous in their diagnosis? I would want to be sure...
Good luck!
Rear diff is a known failure point, sure, but I would look at the parking brakes to make sure the noise from the back wasn't the brake shoes delaminating. If the brakes failed and took out the axles, then I could see the dealer not wanting to replace parts - they seem to like to replace the entire rear axle as an assembly. Quicker for them, expensive for you.
I'm really skeptical that the transfer case would be bad, unless it was already damaged, coincidental to the rest of the story. Same for the front diff. Perhaps the Nissan shop was a bit overzealous in their diagnosis? I would want to be sure...
Good luck!