Hi Schachfreizeit.
Whether you need the entire TTP SC course depends on what you have to achieve in SC in order to achieve your GMAT score goal.
There are a few main aspects of improving your SC performance:
- developing concept knowledge
- learning how to answer SC questions, i.e., learning strategies
- improving execution through practicing
The bulk of the TTP SC course is focused on the first and third aspects, developing concept knowledge and practicing. So, the question becomes that of whether you need to do a lot of both.
Do you need more concept knowledge? Do you miss SC questions because you aren't aware of how certain types of pronouns, modifiers, or other sentence elements work? In that case, your best move would be to proceed through the TTP SC course normally.
Alternatively, if you already know most of the concepts, then you could proceed through the SC course in an accelerated fashion, which I could discuss with you via the TTP in-course chat.
Also, you might get some key ideas that could help you with SC and verbal in general from this video I made the other day.