I know this is a common problem with 98+ 4thgens, but I am now expierencing it myself in my thirdgen after messing with the brake bias by changing the spring weight in the prop valve. The rears lock up now, before they would not.

Now here is the strange thing, the wheel hop does no occur if I put put both feet in ( clutch and brake ). It only occurs if I brake while leaving the clutch pedal alone. I'm struggling to comprehend how this effects the geometry/harmonic vibration/whatever in the rear - but that's a pattern I've noticed.

Either way I'm thinking too much rear brake is the culprit here. I've got koni yellows all around, 800/175 springs front/back with GC weight jacks... LS1 calipers up front as well.

Any input is welcomed here.

 

The reason it happens with the clutch engaged is that you are adding rear brake through engine braking. This effectively increases the rear brake bias.
The easiest thing to do is to adjust your driving, next easiest is to dial out some rear bias.
LCA angles will affect this, if you angle them up slightly to the rear diff you will reduce the effect. You want it so that the LCA is level during braking. Unbalanced Engineering makes a decoupled torque arm that is supposed to alleviate the issue although I have heard mixed reviews.
After adjusting my LCA angles I just drive differently, I make sure to squeeze the brake pedal rather than stab it and try to heel toe and release the clutch as gently as possible. If I feel the rear getting ready to hop I quickly push the clutch in. Sometimes I just skip letting out the clutch until I am easing off the brake.

 

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