valve float

You left out 2 important details. What size are the valves and which springs are you currently running? The manufacturer of the lifters might be handy to know also. Gonna take a stab and say your lifters are pumping up due to insufficient preload. It's not easy to get the preload right with adjustable rocker arms. That and Comp lifters are crap. I say that because the only problem I have ever had with stock hydraulic lifters and stamped rocker arms is that they tend to put a pushrod through the rocker around 7500 RPM.