Your Gmc Seirra has red fluid in the radiator what could it be?

Your anti-freeze is a Dex-cool anti-freeze. It is not compatiable with the green kind. It is a long life coolant which can last up to 100,000 miles. If you have to top off, do not add water as this coolant comes pre-mixed.

Is there red fluid on top of normal coolant? If so you have a leak between you radiator and auto tranny cooler.