After replacing the Master cylinder, the brake pedal goes to the floor

Hello,

Did you have this same issue before the master cylinder replacement?

One of the common causes of the brake pedal to the floor is having air trapped inside the brake lines.
Also, the brake pedal can go to the floor if there is a leak in the brake system.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Just to make sure, have you bled the brake system of all the air after the master cylinder replacement?
Keep in mind that these vehicles will need a scan tool to properly bleed the brakes.

Take a look at this helpful video:

https://youtu.be/nQRnKyVyMuQ

You did not list what model of Toyota truck this is.

Let me know of any questions.
Thank you.