What causes excess moisture inside windshield? Carpet dry.

Condensation on windshield??.. Its common for GM headliners to come loose from late 70's to late 90's year models in a respective time frame. Suprised yours lasted this long, usually about 10 years or less. Dont see it as much from 2000. By the way, is the car garaged at home?

You could have a small leak in your heater core which would put out moisture. Check around heater core, see if any areas are damp,carpet, under carpet. Do you have a slight smell?