Hi, I'm Ted and I will assist you.
The most likely cause of running cool is a thermostat that is stuck open. This will keep the coolant flowing all the time and not allow the engine to get to full operating temperature. This will also cause the heat not to get very warm.
This running cool is not good for the engine. It will lower your gas mileage. and cause excess carbon in the engine and possibly damage the catalytic convertor.
I would have the thermostat replaced and have the coolant flushed.
Its not a real hard job. The thermostat and housing are replaced together. The part is around $25.00 or less and it takes about a half hour to an hour to do. Just make sure you use a quality unit like from Stant of a GM part. Not some cheap autozone part. I have had nothing but trouble with them.
Replacement (4.8L, 5.3L, and 6.0L Engines) Removal Procedure Important: The thermostat is not serviceable separately. The water pump inlet and thermostat must be replaced as an assembly.