[Jim Meyer]

One way to reduce the problem would be to do most of the gear reduction in the modules so that your input shafts are spinning at high speeds with relative low torque.

If you designed them so that the input shafts rotated in opposite directions when going forward for a pair of modules that are steered together the torques would cancel. This could create problems is one of the modules has more traction than the other though.

Neither of these options are easy to implement but I thought I'd throw them out there anyway.