Holley power valves.
 

I have been having a range of tuning issues that had me frustrated, and ready to take it to a shop on my 383 LT1 in my C10. The engine is a smog legal build with a best of everything circle 1994.

On a whim I bought 2 high flow power valves, and I made serious headway again.

So I will say if your running a vacuum secondary Holley with around 450hp. Skip the normal version, and try the high flow.