I'd also try a self test on the DMD (its in your dmd manual). Afterwards, I'd try to reprogram (I mean recalibrate per the instruction manual ) it. Also check to make sure you haven't got any of the DMD wires plugged in backwards to the receiver (i.e. the positive side on the negative side).

Next, I'd swap out the radio with another tank (to make sure the radio isn't the problem) and reinstall if thats not the problem. Next I'd swap the dmd out with another tank and reinstall if that's not the problem, and finally swap the mf unit. It's kind of shotgun troubleshooting, but it works. Sooner or later, you'll find what's causing it. I'd suspect faulty Tamiya electronics last, as they are pretty robust.

You didn't really think you were gonna get to lay around and watch sports on Christmas day did you??