I have a LT1 with unknown springs and a cc306 cam. The car is breaking up above 5500rpm's. I did an opti and it helped some but didnt fix it 100%.

Soooo wantd to know how to check for valve float.

 

take the springs off and have their seat/open pressures tested.
you can throw it on the dyno and see what your curve looks like where you say it's breaking up.

 

On my gen 1 engine i had valve float and the symptoms were loss of power. Like it would pull hard until they started to float and it felt like you backed off the throttle. It didn't break up. That's just what my engine was doing i can't vouch anything except that. How's your plugs and wires??