Dexcool is so bad that even people who work for GM don't use it.
Dexcool, better known as OAT (Organic Acid Technology) has a ton of silicates in it designed to protect an iron block.
Ford's HOAT (Hybrid Organic Acid Technology) coolant has all of the advantages of an organic acid, but NO SILICATES. You are far better off using Ford's HOAT than anything coming from GM.
And yes, Dexcool does cause sludging. GM themselves has acknowledged this and has had well more than a few recalls and TSBs about exactly that situation.
HOAT coolants were specifically developed by Chrysler, Ford, VW, Toyota, Honda, Audi, BMW, Porsche, and other companies specifically for the purpose of being a silicate free coolant. If you are using Dexcool, you are adding silicates to your engine for no reason at all, and these silicates are designed to bond to metal for protection against corrosion, but have no effects on an aluminum block, so what you end up with is silicates floating around your engine with nothing to stick to, but themselves, which leads to clogging of your radiator's passages, and the heater core.
Those of you who use Dexcool, and also complain about overheating in your Mark VIII's might want to re-examine your situation.