Chevy Truck cylinder repair

Hi, recently had to have my 99 chevy pick-up in the shop to replace the cylinder heads/gaskets. I was told there was some issues with GM about the casting of the cylinders in their trucks but I have not been able to find out any info. On line. Also as part of the problem and before the cylinders went completely I was having problems with my antifreeze leaking somwhere. When taken to the shop and tested with dye, nothing showed up. Now 4 months later I have water in my oil. After having the truck flatbeded to the garage, I find out that the cylinders and gaskets leaked. I guess my question is two-fold, one i've heard dex-cool (which i've used for years) has caused lots of problems with chevy motors, etc. As well as GM having casting issues with their cylinders. What do you guys think?