So I've been having some difficulties with my rear axle, and I can't quite figure it out. I have an '04 silverado 2500hd 6.0 CCSB 4x4 with 4.10s in the rear. It's a "new to me" truck, only having it for about 4 months. I've noticed that in any situations of low traction, it doesn't seem like the posi is fully engaging. Some times it grabs, and sometimes it doesn't, giving it kind of a "hopping" feel. I first noticed in some deep sugar sand, so I just figured it was a little bit of axle wrap, and just let out of the throttle, and didn't think twice. But now with winter upon us, I'm noticing more and more. The other night, there was a decent amount of slush on the ground, and during a tight uphill turn, it started to hop again, and clunked like if I broke a u-joint. The thing is, it hasn't made any strange noises since, so I don't think it was the u-joint. I'm at a complete loss. Any help is greatly appreciated.