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.
In order to flush the radiator on my 1996 Safari I had to remove the radiator fan cover under the hood (there are 6 bolts holding it in place). You will find a plug on the bottom of the radiator that has to be unscrewed and the old water will drain. I ususally put a hose in the cap and let the engine run (with the heater on) to flush out all the old fluid…