My Chevy 2001 2500 HD is leaking coolant.

What you describe as leaking sound like the cooler lines but it sounds like the radiator itself may have a problem, it's hard to say what to do to fix t without being able to see the problem first hand. The way an automotive shop would locate the leak is by removing the radiator cap and attaching an adapter that screws on in place of the radiator cap. Something that looks like a bicycle pump with a pressure gauge attached to it is used to "pump up" pressure to simulate pressure generated when the cooling system is at operating temperature, the leak is then found sometimes it is obviously leaking from a coolant hose or cracked housing or radiator.