Make sure your torque wrench is set to 20 ft pounds standard and not metric. There was a buddy of mine had that same problem. He kept blowing his head gasket. Turns out he was actually torquing them to like 3 ft lbs lol

Worst comes to worst get a new torque wrench

i didnt know ft lbs came in a metric version! 
sorry i just couldnt help but giggle