Potential causes of trackpad problems on retina display macbook
Does it act the same on battery power?  Or, can you switch the powersupply plug to the long bulky power cord?

If being on battery clears up this problem, then you may have a ground problem (at least, I have identified this mouse-jerk issue on one mbp).  This is also the cause of the 'tingling' that is sometimes felt when you stroke the aluminium case.

A lack/failure to ground occurs under many conditions.  E.g., power supply uses the direct plug rather than the heavy power cord as the direct plastic power plugs don't transmit ground.  Or, there is a ground problem further upstream (dodgy power board or UPS, dodgy electrics in building).  Or, something metal being touched is actually charged (scary).  Or, some combination of effects.

If not grounded, the voltage inside the Mac "floats" away from ground, leading to weird effects when you touch the machine, as you are effectively a different ground competing for a different level.  And, touching is exactly what you do when using the trackpad.