Since it sounds like you have encountered a muscular inbalance between your chest and your back, and would like your traps to pull your shoulders back... I'd hit some bent over rows, and maybe some wide grip seated rows....
Yes deadlifts are an asset to any back routine, but I think your problem would be more easily solved by a movement that would pull your traps and romboids into the plain you want them to sit naturally...
my 2 bits