first make sure the switch is actually working. put a meter on it and make sure it turns on and off.

is it just the metal bar on the switch without rubber cover. if it does not have the rubber cover cut a piece of hose and slip it over. it will do to things.
give a little cushion every time you let off the brake and it slams into the switch and firewall. and make your switch last longer. and it will add a little to the travel so your switch will actually turn off.
they came from the factory that way but then wear off and they don't get replaced. Hence why you always see trucks with them missing.

after I went thru three switches that solved the problem
my guess is the switch is broken or it is not getting enough pull back to get to cutoff range since they adjusted the pedal.

Make sure your spring is pulling it all the way back.