2005 Chevrolet Silverado Brakes

Front or rear brakes? Do the rear have the parking brake built into the calipers? This guide can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

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

Please run down this guide and report back.

Once you had the pistons reset into the calipers to make room for the new, thicker pads, you had to pump the brake pedal to run them back out until the pads contacted the rotors. At any time did you push the pedal more than half way to the floor? If you did, it's very likely the master cylinder was damaged. Crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Pushing the brake pedal to the floor runs the rubber lip seals over that crud and can rip them. That will result in a low pedal or a slowly-sinking pedal. Those often don't show up for two or three days.