I did my 00 Silverado at 100K and it was about 8 years old. I'd service it with fresh Dex and be done.
Dex gets a bad rep when it really shouldn't. Most car manufacturers changed over to a nylon based gasket and had issue with them distorting. GM was no different. Early versions of Dex did sludge when exposed to air. Overall though our cooling systems should be closed.
If we look at the 3800 LIM gaskets we get quite a lesson in what happened. All nylon, they distort and GM decides to add metal rings by the bolts.
The metal ringed ones distort and GM decides to go with metal frame and the problem is solved.
