Wheel hop in reverse

[FlameOut]

I first drove my truck a short distance a while back, with the bed removed. While backing up, I had very bad wheel hop, but was just hoping is was because of lack of any weight. Well, the truck is now 95% finished, and even with the bed on, I still have very bad wheel hop in reverse. It's so bad, I can hardly back up. This is a manual 3 speed, K10.

What makes it weird is that I can back up just fine if I switch the transfer case into 4 lo (front hubs still free). No wheel hop what so ever if I remain in 4 lo.

I've check tranny and transfer case mounts, check the tightness of the rear leaf springs. Everything seems fine. Clutch, pressure plate and throw out bearing are all new.

Is there something else I should check that I'm missing?