Hard to tell from the pics but it appears the the torque rod arm may have a fairly large lean forward toward the servo. This will automatically induce some differential. BTW - some sill give you a hassle for using those connectors on the servo arms but I won't because I use them too. Just be sure to use the metal retainers and get the screws tight enough.
Try a 6 arm wheel and install it with an arm dead ahead and aft but don't connect to those. Attach to the pair that are toaard the leading edge and see how that works out. This will induce differential.