I'm very sorry you're having so much trouble getting the T-Mobile Rocket to work on your Mac computer and thank you very much for completing all that troubleshooting. It is very important in helping identify the root cause for your issue.
The biggest thing I haven't seen attempted is testing if the software that comes built into the USB stick is corrupted. We would test that by uninstalling the software and downloading the software from our Mobile Broadband software updates page.
Please try that out and let us know if it was successful.
Hope this helps!