1st - 2nd gear differential clunking

I just bought a 2000 Z71 Silverado 4x4.

Every once in a while, after having driven a few miles, there will suddenly apear a bone-jarring shift between 1st and 2nd, accompanied by a great clunking noise from the differential.

The problem will go away only if you turn the engine off, and turn it back on again...which makes me wonder if it it is some sort of electronics problem.

Any idea what's going on here?

Thanks

i had a problem on my 2000 also it was that yoke it would bind then slip. it was from the material it was made out of i bought a new one and put it on and it works great no more clunk.