I would check axle/bearings for slop; if/when good, check hub run-out. A magnetic base dial indicator is a good thing to have on hand. Make sure the hub isn't the problem. What type of sprockets are these? (Azusa makes a variety) A stamped sprocket may warp from the stamping process (axial/lateral run-out), you may be able to tweak/straighten a warped sprocket. If a sprocket seems to be out of round (radial run-out), it may just not be centered on the hub if it doesn't fit the hub tightly. A hobbed/machined sprocket is going to be much better than a stamped sprocket, more money but worth it. There are companies, including Azusa, that make custom machined sprockets. If you're using an adapter/hub that uses kart-type split sprockets, Rocket Sprockets and others make machined sprockets for those (around $18-20 for Rocket).