Try more heat. It needs to crisp at the bottom while staying runny at the top. Don't let them sit in there once done, get them out to stop the heat transfer. I only do one side.
Over easy is easy on cast iron. I tend to put a spoon of butter, spread it a little, and crack the egg into it. The butter should sizzle but not brown too quickly. You should be able to slide the egg in the pan like on a nonstick.