HELP Dodge Charger in limp mode NO check engine light

So I am new to this page, and having some troubling issues with my 2008 dodge charger 3.5l v6. I have read many posts on transmission issues and I still have no idea what is wrong with my car. I was driving down a main road doing roughly 45 mph. All of a sudden my RPM's shot up for not reason. My car is making a noise kind of like shuddering, but it sounds like my car is almost "holding itself back". Having done some research I think my car is in limp mode, and I am assuming it is the transmission but I have no idea why. My car is at 96,000 miles so its nearing 100,000 miles and I know chargers can transmission issues. I am wondering does my transmission sound shot? My check engine light isn't on, and it has never been on yet. I have tried code checking it and nothing. The day my car messed up I checked its fluids and it was extremely low on transmission fluid and oil. I put more fluids in, but it changed nothing, however the fluids are still low. I know the car needs serviced and to be taken to a dealer. I just want some idea whats wrong with my car before I take it in, because I cannot afford a brand new transmission right now, but I'm thinking thats whats wrong. Any input is very helpfull. Thank you!