It should be fairly easy to see if that much coolant is exiting. Is the emissions from the exhaust white and sweet smelling?
I have a 97 Oldsmobile, 97 Lumina, and 98 Lumina. All 3.1L engines. The fact is the head gasket needs to be replaced along with head bolts every 75K miles. I just finished my second head gasket repair about 10K miles ago. THe 2 Luminas have had a repair each.
If you haven't replaced the head gasket yet and you are close to 75K or over. I would think that you are seeing this