5.7, 1996, valve chatter @3000rpms

[dead boat]

I have a 5.7, 1996, thunderbolt V, with valve chatter (it sounds like on the right side) at 3000 rpms while under load only; runs good in the drive way.
I have replaced: water separator, plugs, cap and rotor, and timed it at base timing 10 degrees btdc.

How can I troubleshoot this?

 

[snoski]

Re: 5.7, 1996, valve chatter @3000rpms

Pull the valve cover and check the valve adjustment...

 

[dead boat]

Re: 5.7, 1996, valve chatter @3000rpms

I checked for push rod lash, how much side play should the push rod have when the cylinder is at tdc, I have a slight side to side movement on the rocker arm, it is consistent with all the valves when each one is at tdc.

 

[dead boat]

Re: 5.7, 1996, valve chatter @3000rpms

Head gasket blown between 3 and 5, thank all who have helped.