Combination hydroboost/engine vacuum question

[earl84]

I have a 66 C20 that I installed a 454 and TH400 in, daily driver. I installed a new hydroboost unit and all new brake system from a '79 C20.

To be honest, the brakes have never been right. They have amazing stopping power, but once the truck is fully warmed up, the brakes get "grabby" when I stop, just like having a warped rotor. I have had rotors turned, put a micrometer on them, and everything is running true. OK, next thing was a possible bad combination valve, replaced it, same thing. I figured that maybe the power steering fluid is getting hot causing it to foam up and introducing air or something. Changed to Royal Purple fluid, installed a PS cooler, better maybe, but still grabby, especially when coming to a slow stop at lights, to the point where the left front will sometimes lock. I've also replaced the calipers.

Here's the engine part. I am thinking I want to just go back to a vacuum brake booster, so I put a vacuum gauge on yesterday to see how much I had. The gauge sort of jumps around between 14-19 at idle, not steady at all. I don't know how much I should have for a vacuum booster to begin with, but seem to recall that 14 was a minimum. Had the gauge hooked up to full vacuum on the same port as my vacuum advance (I disconnected it and plugged vac gauge there).

Any thoughts from anyone, either on going to vacuum booster, other components, engine vacuum, etc? Thanks.