Ok, so if the upper radiator hose is getting hot, that suggests that the thermostat is opening in some capacity.
If the heater hoses are cold, that suggests either a blockage or lack of flow, such as the impeller on the water pump failed, or eroded away, etc.
Probably the easiest way to get a basic idea is to disconnect the hose from the intake manifold, hook a temporary hose a few feet long draining into a clean bucket from the manifold outlet, start the truck, it should begin moving coolant through the hose, regardless of thermostat position. If you have fluid movement from the manifold, reconnect and disconnect the heater core to radiator hose, plug the radiator hole, then hose into a bucket and run the truck again, if no flow into bucket, suggests clogged heater core, potentially a hose/obstruction.
If you don’t have any movement of coolant in the first test, investigate the water pump, and radiator hoses. Coolant does degrade over time, most people let it go way longer than it should, silicates in the coolant, along with external debris that made its way into the system can erode/corrode a steel impeller over time, or with straight water, rust, to the point the fins are totally gone. The pump doesn’t have to weep or leak to have failed.
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A thermal image gun or a temp gun is useful to for this type of diagnosis.
Also, a lean fuel mixture or late ignition timing can cause overheating too. With the heater core being cold, I don’t believe that is the main/root cause in this scenario. Just something to note.
Here is a couple pictures from the net on what can happen to an impeller:
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