I installed the app... and gave perms for TD to see my account but don't my existing GTasks get loaded?
Unfortunately, there is no integration between Google Tasks and Todoist. Due to the lack of most of the features that we have which Google doesn't, a direct sync between these two would be almost impossible as a lot of data would be lost during syncing (lack of support for so many task properties by Google).
Nonetheless, we will consider implementing a way to add tasks from Google to Todoist once (as an import option) in the future. For now, you're welcome to install our Todoist for Gmail plugin https://todoist.com/gmail which will appear just as Google Tasks in your Gmail and offer a lot more features :)