2004 Silverado Smoke from ventilation

Mileage :81250 - Due for an oil change over by 500 miles Yeah I know! :) Rear wheel drive, Well maintained just been a bit busy to get by an oil change place. All gauges reading normal. Coolant a little low but with in norms.

Problem:
Yesterday on the way home from work while on the Highway I started Coughing and then I noticed a White Smoke coming from the vents. I shut the air conditioner off and rolled the window down.

Shutting the air off stopped the smoke. Got home, did not find the Radiator steaming off - I had an older car do that once. No broken belts, all fans working well. Still getting cold air from the conditioner. Have not tried the heater.

It rained yesterday where I live and work, I drove to work today and nothing seemed up. I am at a loss of what it could be.

Any ideas would be great

Thank You.