Try replacing the bushings and the pivot cups. If you prefer tighter trucks, buy harder bushings instead of cranking them down (overtightening the kingpin and squash and irretrievably deform bushings). Besides Bones, there are tons of other bushing options as well. Maybe try a few and see what works best for you.
If that doesn't solve the problem, take off your wheels and check to make sure you don't have a bent axle. Maybe this isn't a super common problem, but it can and does happen.