OK. I will provide you step by step what i did and what Tascam had me do in hopes that it helps you figure your issue out. If this doesnt help you resolve your issue, i recommend contacting Tascam yourself.
1. I installed the MAC version of the firmware and drivers from the disc that came with my Tascam US-144 and once completed, plug the US-144 into the Mac. The app for the US-144 said that nothing was attached or it couldnt be found. Something like that.
2. So i downloaded the latest driver from the Tascam website. This showed up some feautres but not all. The latest drivers were for the MkII.
3. I had reached out to Tascam about this especially since it is so confusing to figure out what to download on there website. There is no consistancy with there naming convention for the drivers and firmware.
4. While on the phone with Tascam support, we uninstalled all versions of tascam craziness and installed just the file for the MkII.
So to be clear, i had to install a driver for a device that i didnt purchase for it to work. I have the US-144 and the driver for the US-144 Mk II is the only one that would make it work.
5.I restarted my MacBook and once i was logged into the Mac i plugged the US-144 into it and opened Garage band and was able to use it to control Garageband.
I did however notice that if i plugged in the US-144 before turning on the Macbook, the US-144 was never seen unless if i unplugged it and plugged it back in.
I hope that helps.