No brake pressure

Welcome to 2CarPros.

It sounds like you have done a lot. If you have properly bled the system, I suspect the master cylinder is bad. If the brake pedal went to the floor when the line broke, I have often seen where the plungers in the MC travel beyond their normal track and are damaged by corrosion in the MC. As a result, fluid bypasses the plungers and the pedal goes to the floor.

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

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Here are the specifics for replacement. The attached pics correlate with the directions. The directions are for the basic vacuum boost system. If for some reason (and I doubt it) this has the hydro-boost system, let me know.

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2005 Chevy Truck Silverado 1500 4WD V8-5.3L VIN B
Master Cylinder Replacement (Vacuum Boost)
Vehicle Brakes and Traction Control Hydraulic System Brake Master Cylinder Service and Repair Procedures Master Cylinder Replacement (Vacuum Boost)
MASTER CYLINDER REPLACEMENT (VACUUM BOOST)
Master Cylinder Replacement (Vacuum Boost)

Removal Procedure

Caution: Refer to Brake Fluid Irritant Caution in Service Precautions.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.

1. Apply the park brake and block the wheels.
2. Disconnect the electrical connector from the brake fluid level sensor.

pic 1

3. Disconnect the brake pipes from the master cylinder.

4. Important: Install a rubber cap or plug to the exposed brake pipe fitting ends in order to prevent brake fluid loss and contamination.

Plug the open brake pipe ends.

pic 2

5. Remove the master cylinder mounting nuts.
6. Remove the master cylinder from the vehicle.
7. Remove the master cylinder reservoir.

Installation Procedure
1. Install the master cylinder reservoir.
2. Bench bleed the master cylinder.

pic 3

3. Install the master cylinder to the vehicle.

4. Notice: Refer to Fastener Notice in Service Precautions.

Install the master cylinder mounting nuts.
Tighten the nuts to 33 Nm (24 ft. lbs.).
5. Remove the rubber cap or plug from the exposed brake pipe fitting ends.

pic 4

6. Connect the brake pipes.
Tighten the fittings to 25 Nm (18 ft. lbs.).
7. Connect the electrical connector to the brake fluid level sensor.
8. Bleed the hydraulic brake system.
9. Release the park brake and unblock the wheels.

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Let me know what you find or if you have other questions.

Take care,
Joe