I have a solid knock during idle...sometimes it even wants to stall. Then at high RPMs it chatters. My guess lifter(s) gone bad. Any help?

 

Valvetrain noise will be from a light "click" to a medium "clack" sound, but never a clunk.

A low knocking noise is bottom end problems.

Like was told to me by one of my early techers of automotive wisdom: You won't have to ask if it's bottom end knock. You'll know when you hear it. He was right.

Flat tappet cams don't usually make a lot of noise unless the lifters are bleeding down or the valvesprings are floating.

GM roller cam setups make a fair bit of valvetrain noise even if they are working right.