occasionally when I use the brakes the pedal goes to the floor and have no brakes I can pump again and get brakes. Petal shutters when this happens. Have replaced front calipers and brake hoses and changed fluid.

 

Master cyl is defective !
Don't forget to bench bleed the replacement master cyl before installation !
Good move to bleed all wheels also being careful not to wring off the bleeder screws on the older wheel cyls.
Double check the connections for the front wheel speed sensors if you disturbed them.