I need detailed instructions for replacing the heater core

Ok remove dash and instrument panel as suggested. Then Service Information
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2000 Chevrolet C Silverado - 2WD | Sierra, Silverado,
Heater Core Replacement
Removal Procedure
1. Drain the engine coolant. Refer to Cooling System Draining and Filling in Engine Cooling.
2. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging.
3. Remove the heater/vent module. Refer to Heater/Vent Module Replacement.
4. Remove the heater core cover screws.

Object Number: 363771
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5. Remove the heater core cover.

Object Number: 363772
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6. Remove the heater core.
Installation Procedure

Object Number: 363772
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1. Install the heater core.

Object Number: 363771
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2. Install the heater core cover.

Notice: Refer to Fastener Notice in Cautions and Notices.
3. Install heater core cover screws.

Tighten
Tighten the screws to 1.6?NÂ m (14?Lb?In).
4. Install the heater/vent module. Refer to Heater/Vent Module Replacement.
5. Recharge the A/C system. Refer to Refrigerant Recovery and Recharging.
6. Refill the engine coolant. Refer to Cooling System Draining and Filling in Engine Cooling.
2. If equipped remove the auxiliary battery. Refer to Battery Replacement in Engine Electrical.
3. Disconnect the heater hoses. Refer to Heater Hoses Replacement.
4. Remove the accumulator. Refer to Air Conditioning Accumulator Replacement.
5. Remove the instrument panel carrier. Refer to Instrument Panel Carrier Replacement in Instrument Panel, Gauges and Console.
6. Remove the HVAC module drain hose.

Object Number: 499156
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7. Disconnect the electrical harnesses and the ground connections as needed.

Object Number: 363009
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8. Remove the mounting nuts and the screws from the HVAC module.
9. Remove the HVAC module assembly from the vehicle.
Installation Procedure

Object Number: 363009
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1. If you are replacing the HVAC module, transfer the components from the old HVAC module as necessary.
2. Install the HVAC module assembly to the vehicle.

Notice: Refer to Fastener Notice in Cautions and Notices.
3. Install the mounting nuts and the screws to the HVAC module.

Tighten
†Tighten the mounting screws to 4?N m (35?Lb?In).
†Tighten the mounting nuts to 9?N m (80?Lb?In).

Object Number: 499156
Click here for detailed picture of above image.
4. Connect the electrical harnesses and the ground connections.
5. Install the HVAC module drain hose.
6. Install the instrument panel carrier. Refer to Instrument Panel Carrier Replacement in Instrument Panel, Gauges and Console.
7. Install the accumulator. Refer to Air Conditioning Accumulator Replacement.
8. Connect the heater hoses. Refer to Heater Hoses Replacement.
9. Install the auxiliary battery. Refer to Battery Replacement in Engine Electrical.
10. Fill the cooling system. Refer to Cooling System Draining and Filling
hope that helped and yes im a gm mechanic:)