[Fasty67]

Both suggestions above are a great start. Make sure you're maintenance is up to date. unfortunately since you know nothing you kinda gotta do it all. The on thing I would add is that the 5eat automatic transmission DOES have a filter that you can change and I would highly recommend that you do so. It cannot be had from the dealership or a parts store you need to snatch it from Ebay. You will need almost 6 qts of Subaru or idemitsu HP transmission fluid.

 

[Fasty67]

What was the condition of the trans fluid that was removed? The filter is easy although it does require dropping and resealing the pan. I can't say my symptoms were the same that you are having but I've done two filters two whole fluid changes and two drain/fills in total on my transmission and its performance has improved quite a bit.

 

[Fasty67]

My issues were lazy shifting, inability to hold gears(early shifting) and a random intermittent rpm drop with a thud feeling. All symptoms remedied through a series of fluid AND filter changes. When fluids break down their shear point causes them to be ineffective here's a link to a good read that explains that and why several people recommended that you change your fluid. Shear Stability and Viscosity Loss
It seems as though your transmission is beyond just having a fluid breakdown problem and you likely have a mechanical failure. Now you'll need to have a qualified technician do advanced diagnostics on your transmission to determine what needs to be replaced through a series of complex procedures.