So, I was just driving in a parking lot one day and my van made a thump sound, and I thought nothing of it until I started driving home. The speed limit was 55 and once it got to about 37 it started revving but wouldn't go faster. I took it to advanced and their computer said to change the solenoid so I did that. It drove FINE for a day and then the same thing happened again, so I complelty changed the transmission fluid and the filter and gasket. It drove fine and the check engine light went off until it got up to 40 and it revved and thumped but went into gear and was able to drive to the store and on the way back home it went into limp mode again and will not go faster than 35. I turned the key 3 times and got P0700 which isn't a very specific code, it just means somethings up with the transmisison. What else can I do?