Charlie,
You are correct about the air/high temp problem with Dexcool. That problem has been acknowledged by GM.
The gasket eating properties are a myth. The real problem is that GM Powertrain designed some really crummy intake gaskets and they flat fail. When the cooling system gets low enough, the engine overheats and then the head gaskets fail. Those same engines used Dexcool ........and the Dexcool often gets incorrectly blamed. But, if you read it on the Internet, It must be true!!
I have Dexcool in my current Duramax equipped truck and used it in my last DMax truck. Never had the mud or any gasket problems in either....Why? Good gasket design and then system never ran low.
I have a friend who is the Service Manager at a CAT dealer. They regularly use liquid dishwasher detergent to flush diesel engine cooling systems. I've never tried it , but I'll bet it works well.