Brian
sorry I didn't see your message sooner.
Are you using ground control points? Without ground control, your mosaic may be off by many meters.
You get the best accuracy if you can survey points that are visible in the imagery using a high quality GPS receiver, then import the control points into D2M, "link" the control points to the images, and re-run your orthomosaic.
If you don't have independent GPS control points you can extract control from the Esri imagery basemap. This will ensure your mosaic will align with the basemap but be aware that our basemap comes from many sources and Esri can't provide a stated accuracy for the basemap.
A third option (if inside the USA) is to use the NAIP image service to extract control.
Cody B