02 Suburban low coolant problem

I have a 2002 Suburban with 100K miles. I just pulled a pop-up camper through the mountains of Utah and Colorado. The trailer was well within the towing capabilities of the Suburban, but we did pull a few tough grades in 2nd gear, and did push out a little coolant, which I replaced. The temp never rose above its usual level. Now that I am unhooked from the trailer, I am pushing out some coolant even after driving 10 miles in town. I just got a low coolant message, but when I look at the coolant reservoir, it does not appear that low, and my temp level is still normal. Any ideas. Thanks

Has the overflow cap ever been replaced? Pressure is important in the cooling system. I replace mine every 3-4 years.

I know that when I flushed the cooling system, the sensor was sticking and reporting low coolant after refilling the system. I tapped the side of the overflow tank and the light went out and never came back on.

//2000CAYukon

Thanks. I found out the area around the sensor is leaking, which explains my apparent overflow and possible malfunction of the sensor itself.