What cam and springs are you using?
Valve float will chew up a lifter and cam.
2001 ws6, 40k miles, Ls3 416 stroker, short block built by PER the rest by me. LPE Ls3 heads milled to 12-1 comp, FAST 102, NW 102, kooks 2", dual DMH cutouts, Magnaflow C/B, BTR cam + springs. Full UMI suspension.