Are you still using a brake booster? Sounds like the
seal in the plunger inside the canister is hanging up.
Could also be the vacuum valve in the booster is
leaking air to the can and applying the brake.

Remove the booster and and install a brake booster
bypass. Its usually two unions and a short 4 inch
brake line with the proper ends. Be careful and
you may only have to bleed at the last union.

Now drive the car. You’ll have to push the pedal a
bit harder. If the brakes work fine, your problem
is in the booster. Most race car drivers race their
Alpines and Tigers without the booster. They are
just too unreliable.

If the brake problem persists, you’ll have to think
about (1) a weak pedal return spring or (2) A weak
or broken spring in the master cylinder.

The brake light switch is hydraulic and notorious
for failing or no turning the brake lights on unless
you push hard on the pedal. Easy stop can lead
to some idiot running into you.

Go to http://www.TigersUnited.com and look up how
to replace that switch with a modern electrical
switch. A worthy modification.

Dave Johnson