[acammer]

Unfortunately it sounds like you may be a victim of "you get what you pay for". I went and took a peak at TSP's site, it looks like the Comp lifters are only $266 - that's even less than what a set of GM stock lifters cost! Great deal if they hold up, but I think you're finding that they don't.

I would consider a genuine GM LS7 lifter (not Delphi LS7-style) to be the minimum acceptable lifter for anything that runs .600+ lift and 400lbs of open spring pressure. Lifters are the most common component in the valvetrain to fail in my experience - and also the most difficult and costly to service. When I build out a package for our customers I default to the Chevy Performance - Racing lifters (aka Caddy, GMPP, P/N 88958689). These are another $130 over the cost of your standard genuine GM LS7 lifters (what all of your non-dod lifters are), but these are a substantially better quality part, better materials, better check ball mechanism, and much better reputation for coping with the rigors of higher lift cams, with more aggressive than stock lobes, more spring pressure, and more RPM.

Inexpensive lifters tend to create expensive failures. It's definitely a component worth investing in up front to save yourself a headache down the road.