Transmission Problem

Okay. First I have a 1992 Mercury Sable with 240000 miles on it. The car just recently started to do this. I would go to take off. It would drive fine. But maybe after a sharp turn, or somewhat of a hard acceleration, going from first to second seems like it slips. It would grab. Then after that, *normal driving* going from first to second would be fine. But it would take second to go to third about 3000 rpms. After that it will go to third and directly to forth. And when this all started happening, The tourque converter lock up quit working. The fluid was a little low, but I have added some and got it back to to the top. And yet it still does that. I know that it could be the trans getting ready to go out, but I don't have the money to fork out for a new tranny *or a junk yard tranny* If anyone has any idea, please let me know. It owul be greatly appreciaited.