GM has been using the hydro boost system in their light duty trucks, especially the diesel powered ones starting in 1988, I own 3 of these trucks with hydro boost on them. Two with disc/drum (K3500), and one with 4 wheel disc brakes (3500HD). other than a leaking boost unit (O ring seal), they have worked flawlessly, and all the trucks have over 250,000 miles on them. I don't have the on/off feel whatsoever, even in snow........
I've also driven an Astro van with the hydro boost on snow, no hint of brake lockup, and if you're going to have modulation problems it will show up on ice/snow surfaces quickly.
My next street project will have hydro boost likely pirated from a GM light duty truck on it. Probably from a 3500HD with 4 wheel disc brakes.
BTW, all of my trucks do have a fluid cooler on them from GM, so likely it is needed in the system to operate properly.