I used an old DZ-123 for my decoder on the cheater chassis, but its the same Tomix TMxx motor/mechanism. No trouble at all, runs smoothly, etc as one would expect from a DCC install, ie normally. And the Digitrax DZ123 is their el cheapo, can't power much decoder. I'm sure the TCS M2 would handle more power so it can't be a current draw issue in terms of the motor itself. I didn't use any resistors or anything on the motor, just set Vmin and Vmax to appropriate values to bring the speed into reasonable limits.
Perhaps you have a short somewhere? Perhaps between some weight and one of the pickups? I have 2 of the Whitcomb kits at hand and one of them partially built. There's much more chance of a short than in the design of the cheater chassis which lets you just pile tons of weight on top of the casting since its still hidden inside the boxcar shell.
