Remembering my old hotrodding days. We used to run some high lift, long duration cams that would give vacuum problems if you had power brakes.
I had one Olds 442 with a 350, 308 duration, 472 lift cam. It would get the hard brake syndrome because of low vacuum.
I wound up putting a vacuum cannister on that car. It was just a little storage cannister that would hold reserve vacuum for the brake system.

I wonder if something like that would work for the SS problem.

 

I feel better about it now that I know what it is and found out I can stop, it just feels different until vacuum builds up. The first time it happened, there were several cars just outside my garage and I had to be careful to miss them. They only left me a very narrow way out and I thought the brakes had failed at first.