Brake pedal goes almost to floor but brakes do stop truck

I replaced the rear wheel cylinders because the bleeders were broke, replaced the master cylinder because mechanic said it was the issue also replaced the ABS unit. Bled the system from back to front. The front calipers and pads were replaced just prior and truck sat unused for one year just before parts were replaced. The brake pedal now goes to floor, I can pump the brakes up with the car off and as soon as I start it the pedal goes to floor. I have tried to bleed the brakes again but pedal goes to floor. I did bench bleed the master and checked to make sure it holds by plugging the lines and pushing on rod with screwdriver. Not sure if the ABS unit is holding air causing my issue. Help!