To properly identify the cause of the slowdown, you really have to go through a thorough troubleshooting checklist. Slow even when not connecting to a shapefile, probably means it has nothing to do with shapefiles because Tableau doesn't do anything special when doing so.
If possible, I would suggest the following actions:
- To mitigate this problem -- are you able to work with an extracted datasource instead of a live connection? That should certainly lead to performance benefits.
- What exactly is the shapefile you are working with? The level of detail of the file could cause slow rendering performance; but this does not explain a slowdown when not working with the shapefile.
- Rebooting your machine
- Closing other applications; especially resource intensive applications like security scanning software, etc.
- Clearing the local query cache
- Reinstalling Tableau
Have you tried any other trouble-shooting steps?