1 Interference from the UC or Gatling guns can cause it to run wide.
2 bad ultrasonic. or bad (loose) connection at the VT board. Also make sure it is not dirty.
3 Arch buffer ,or keep out settings set to wide on your VT board.
4 recalibrate... do this regardless,it may have not been a good calibration when you installed the new VT, this is always the first thing I try when the UC is not measuring.
Try this.. use something to block the US ,then measure back to it.I will us a big garbage can ,at 17 inches. check the VT board lights,then back up the target 17 inches ,another light should come on, keep repeating to see if the US is measuring correctly. You may find that the further away you are the less accurate your US is.
On the drivers side ,at our locations people generally park left center ,and the machine will run to its limits. Another test would be to use a narrow car ,put it on test mode ( so there is no interference from UC) ,and pull in to the right a few times to see the measure. what I am trying to say is this ,you could very well not be measuring the DS at all ,but only see it few times a day because people are to the left already.
Hope this helps a some.