Shifting prints are most likely caused by improperly tensioned timing belts. If the belt is too loose, or even too tight, the belts can actually miss turns on the motors. In general, belts should be tight enough to minimize slack, but not so tight that they start placing a lot of stress on the motor shaft or pulleys. Once a belt is on, turn the motor pulley with your fingers to gauge if there's too much resistance. If the belt makes an audible noise when you 'pluck' it with your fingers, it is too tight.

The Thingomatic operation should be nearly silent. If your motor makes a humming or buzzing noise, your belts may be too tight. Please consult this page for further detail: http://wiki.makerbot.com/thingomatic-doc:about-timing-belts

While we’re talking about fine tuning your machine, it’s important to make sure your stepper driver voltages have been adjusted for optimum performance. Too much power and your motors will run hot, but too little power and your motors won’t respond or have the right amount of torque. You don’t want to be missing steps, so make sure to check this guide for proper calibration: http://wiki.makerbot.com/thingomatic-doc:calibration