Even though your wheels and tires will show a "Balanced" condition on the balance machine, you shouldn't rule them completely out. I have a similar situation I went through the entire drivetrain, driveshaft, axles, rotors, drums, etc. and found that the magnum 500 wheels were the problem. They would balance out just fine but when you spin them by hand on the balance machine, you could see them wobble side to side about half an inch. Put some "known" good wheels on it and see if it changes anything.

Dave