How much load are you using for shrugs? Your traps are phenomenally strong. It is not unreasonable to be able to use 2 x bw for quite high reps (>10) after you have trained them for a while.
Power cleans and clean high-pulls are also excellent trap builders. Cleans are such a ballistic exercise that even using lighter loads than you would for shrugs requires a very powerful contraction of the traps in order to accelerate the bar.