Have quite a few issues with my '05 Subaru Forester X and don't know much

Hello everyone!! I'm new to the forum and was needing some serious help on my 2005 Subaru Forester X.

I know I need a new transmission or something along those lines because sometimes it feels like the transmission is slipping when I go to accelerate and the AT drops into the next gear. I genuinely don't know what to do and I know that forums can help out quite a bit because everyone has some information to share, so please if anyone could help me out that would be amazing!!!