Want to build maximal grip strength along with stronger traps? Get heavy loads in your hands near your maximal capacity.
Grinding away hundreds of reps on shrugs using a half-inch range of motion won't cut it. It's just not a good use of time. The deadlift is. The deadlift is probably your strongest absolute lift. Milk it for all it's worth instead of letting hundreds of pounds of iron drop to the floor.
The trap bar deadlift with a shrug at the top will build full body strength plus overload the grip in the process. You can do this with conventional and sumo barbell deadlifts as well.
The shrug challenges your grip more than anything in this position. You're accelerating the load down as you let the shrug descend towards the floor. That will make your grip recruit even more force to stabilize the load, hence overloading the movement from the hands up.
Get in as many good reps as you can and you'll be surprised at what just a few reps of shrugs at the end of a top-end deadlift set can do for your grip strength and trap size.