1998 Nissan 200sx transmission

I have a 1998 Nissan 200sx. It is an automatic. I accidentally shifted into reverse while going 40 mph. Now it will drive but it starts off in what feels like 3rd and it will shift in and out of overdrive. Also, when it is driving, sometimes the car feels like the engine is getting pushed against and bogs down. All I have to do is take my foot off the gas and put it back on, it is fine. I can get the car up to 80 mph. When I try to shift the into first gear manually, it rocks backwards and there is alot of pressure against the engine and it does not want to accelerate. It also feels like there is shaking going on in the transmission. What is wrong with my car?