Brake pedal goes floor. Changed brake booster, no change. No visible leaks. Also, bled the brakes. Pulled vacuum hose off brake booster and covered with tape and I get resistance. All new pads on back and front. Confused

Try bleeding the system again. Likely you have left air in the lines if you see no leaks. Remember to start with the wheel that is furthest from the cylinder and work to the closest.

There is likely a valve that distributes fluid to the rear vs front brake cylinders or calipers. I would investigate that, after you follow the advice of Taver.

I have had this issue and spent two days bleeding the breaks changing calipers and I also bought a master cylinder. but tried one last thing before I installed it. the brake pads were backwards . not with the wrong side facing rotors but the brake pads that I had on the outside of the rotor needs to go on the inside. never ran across this problem before in my life . but once I switch to brake pads around the car stopped on a dime

I have a 2002 Bonneville my front breaks and rotters need changed I carefully moved my car for the trash man and I heard a bad noise when I was reversing and the break peddle went to the floor going backwards I can barely stop. !! Any advise?? Do I need a new caliper for the rear