I put a shim between firewall and mc. Used a pretty thick metal washer. Took it for a drive.....very little pedal. So little in fact I turned around and came home. Removed thick metal washer and inserted instead some gasket material I cut out. Went for a drive. Much better pedal of course. Went on a route that included plenty of stop signs so I could give the system a real workout. Problem did not reoccur! Could that very little difference in pushrod travel the thickness of a gasket have been the issue like Doc said? Not ready to say all is well quite yet but going on a long drive today so we shall see. I'll be jiggered if that 1/32 " in pushrod length was the problem.