Sounds like a perfect batch of Brownies to me.
What kind of oven do you have? Is it an older oven? The thermostat could be off and it might need to be serviced.
You can buy an oven thermometer As Bolas suggested. You just hang it on a rack.They aren't that expensive. Go by that thermometers reading. If the oven is seriously off in temp have it checked out.
If your with me that's great. If not. Get out of my way.