Heater comes on and off .This is not normal.could this be switch? Somethingelse?

What is your question?

You can be driving along with the heater working, the all of a sudden it will quit. Then it will come back on. Slowly getting worse. It did this 4 times, spread out in a four hour period

How long has your 1999 GMC Yukon had this problem?

Just started a week ago