MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
Try limiting retraction length to 4.5 max, and increase retraction speed to 60mm/s. If your filament keeps getting grinded, limit retractions and increase retraction window. Increase the temperature a bit (5-10º) may also help (the higher the temp the lower the force needed to push the plastic through the nozzle). You could also try an extruder with tension control, as the one I designed, and lower it a bit, so the filament does not deform that much.