My car is stalling at random times

So a couple months ago, my car was having troubles driving under load. I would be going up hill and it would sputter trying to go into the next gear and it would make it feel like the car was jerking around. I just drive to school/work and back so it is not like it is doing hours of driving at a time. One day when I got out of school a engine light had come on. I called my Dad letting him know, hoping that it would solve our issue, and two minutes down the road it stalled for the first time. I was going about thirty KmH. After we got it home, my Dad checked the code and it read as the throttle position sensor, so we replaced it. It stopped jerking around when shifting into new gears under load, but now it will not shift, and the check engine light is still on and still reading the TPS, so we got a new one, since I had read that sometimes the new ones come faulty. The engine light was still on. The other day I was driving in the parking lot and it stalled again, but this time I could not have been going more then ten KmH. It is only having an issue changing gears at around ninety KmH and when I am going up hills, and the RPM's just seem to be stuck at around 2,500 so it i's not red lining or anything. Any help would be appreciated!