One solution i have heard of is to get a shortish shock absorber and weld a mount somewhere to the snout of the diff at one side and the other mount through the floor. works (obviously) by absorbing the forces of the torque effect(when the diff snout goes upwards under acellaration)and where tramping it is going up and down really quick... dont get too stiff a shock though cos it will then try to flex elsewhere(control arms etc),
drastic i know but you know what they say about desperate times.