'00 Suburban 5.3 Rear End Issue?

I have a 2000 Chevy Suburban 4x4 5.3L with 110k on it.

Recently, something towards the rear end of it makes a loud clicking sound every few seconds and it has gotten worse. A couple days ago I was on the highway and the car suddenly made a very loud grinding sound and would not accelerate. I pulled over and was hitting the gas, the speedometer said I was going 40-50 miles an hour but the Suburban wasn't moving at all. I put it through reverse and all gears and it clicked back and thankfully I got it home. I haven't driven it since then. I checked the transmission fluid when I got home and it's fine. The loud clicking and grinding sound comes from the back of the car.
Anyone know what this could be? Thanks.

From your post I'm surprised you even got it home. Need to have someone look at the rear differential and/or rear axle shafts.

This is just a guess based on your post.