Sorry for the late reply. I've been pretty busy.
I got around to adding new gear oil. It took quite a bit too fill so it probably was low. But it didn't do anything to help the problem.
Eventually I ended up replacing the transmission. This was mostly due to the car no longer shifting into reverse, and having trouble shifting into other gears. While it fixed the shifting problem it only partially fixed the slipping. But at least it seems to have helped some. It still slips a little but not nearly as much. It might just need a new clutch now, I'm not sure.
I should have replaced the clutch while I was changing transmissions but I got impatient since I would have to wait a while to resurface the flywheel. I figured it would be fine with its current one since it was relatively new. Unfortunately I have to put this problem on hold for the time being since now the car is having other issues with overheating.
I just wanted to thank everyone who gave me advice on this. If your interested in helping me figure out my latest issue, here is a link to my new thread
https://zilvia.net/f/showthread.php?...62#post6390462