Is it moving slightly becuase the size of the part is changing slightly? Pro/E tends to alter it's zoom based on the size of the part. If this is the case, then try making a datum feature of a fixed length slightly larger than the part and layer it off of the screen. That way Pro/E will think the overall part size is a fixed size.
You can use a datum plane, then redefine it's attributes to fit to a particular size, or use a datum curve.