How do I replace heater core in 98 chevy silverado? Heater blows fine, just not getting hot.

Question edited for clarity and typo, and add maker.
Question moved to model category.

The AC evaporator core and the heating core are normally two separate items. It is unlikely that the heater core is completely clogged. There must be a valve in your flushing circuit.

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https://www.google.com/search?q=2000+Chevy+Silverado+flush+the+heater+core

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1: not enough liquid in the system (air in the heater core)
2: inoperative heater valve not allowing hot liquid into the core
3: hot/cold blend door in the heater box stuck on cold
4: clogged heater core
A clogged heater core will have one hot hose and one significantly cooler hose at the firewall connection; easily tested by hand. a good core will have both hoses very hot to the touch when the heater is on full blast.
Make sure that the system is full and at operating temperature, and the heater controls set on full heat. Feel the hoses at the firewall; if they are both too hot to touch then the problem is in the heater box or controls.

Check the water control valve . It most likely isn't letting coolant into the core.

I would check that the heater core at the firewall is getting hot with the engine temperature. If not, then the heater core is plugged and needs to be flushed or replaced.

Also, if the heater core is hot at both tubes, then it's a heater blend door problem having to do with the vacuum motors.

1.)heater core restricted-check both heater hoses coming from the heater core if one is cold your heater core is restricted and you will need to flush the core.
2.)Your air mix door actuator in the vehicle is inoperative and you will need to replace it.It is located on the bottom of the heater case in the center of the vehicle.It mounts straight up with a couple bolts.

MAKE SURE ALL BLEND DOORS UNDER DASH WORK PROPERLY. GOOD LUCK MOTOR62500. PS ARE BOTH HEATER HOSES HOT?

once truck is warm check both heater core hoses to make sure they are both warm if not then check the cold water valve could be stuck shut not allowing coolant to travel in to heater core.

Your heater core is probably getting plugged up. THis is a common problem with any car as the flow through the heater core is not as much as through a radiator which causes silt deposits in the inside of heater core itself. If you replace that your problem should go away. You should be able to feel a difference in temperature of the coolant in the supply line versus the return line going to the heater core. If there's a dramatic difference then the core is plugged.

Check blend door actuator for operation

Check your Heater Core