Small Block & Big Block Chevy Specific - aluminum corvette '89 heads on 350 w/mild cam

I've installed the 10088113 heads on mild rebuilt 350,with 1.5 roller rockers and stock pushrods and lifters[hydraulic],I was turning to about 6000 rpm with iron heads with same valve size 190 int,
Now it starts breaking up at 5000 rpm,but makes better power up to that point,1/2 second quicker in an 1/8 mile,But I'm worried at why it starts popping at the early rpm,than previously wasn't a problem....used same HEI at first,then went to an Accel w/ amsd coil and new Taylor wires and rapid fire AC plugs #5s....

Possible valve float???

Check for detonation. The L98 heads have extremely small combustion chambers - 58cc.

sorry to sound like such a newby.....but thought of detonation also,but researching made it sound like pinging,which i'm familiar with,at diff rpms,but high rpm popping?? noise?....and way back when i seem to remember reading of det occuring,without the pinging as warning,but todays articles don't seem to address it...
plugs weren't glazed or have slag[this after a dozen test runs at those rpms,...just installed those heads and tried adjusting the valves lightly,going with slight drag on pushrod and then 3/4 turn,on cold motor,wonmdering about the 20=22 ft pd torque method but thats alot of stud nut travel compared to my first method,which my friend has said may be overtightened even and the cause of ruining me cam lobs....but I've too much mechanical experiance to think my first method was overdone.....Any good valve methods,or should I be scared of the torque wrench method for these heads....considering thye ls1 etc use this method....what makes these zz4 heads diff???
Thanks

I was turning to about 6000 rpm with iron heads with same valve size 190 int. Now it starts breaking up at 5000 rpm, but makes better power up to that point,1/2 second quicker in an 1/8 mile, But I'm worried at why it starts popping at the early rpm, than previously wasn't a problem....

Sounds like either a collapsed lifter, or simply the way you set your valve-lash. Remove both valve covers, and check to see if a pushrod came off of any of the lifters (you'll be able to pull it out, if so)....