Those of you continuing to have issues, give this thread a read:
-For everyone having connection issues of various types: UPDATE 6-9-24
This has been updated recently to correct broken links. Blizzard had removed links for the original tools, so this has been updated to still provide you the tools you need.
Try to run some of these tests if you can, especially while encountering issues if possible.
You can post your results on this thread.