1995 Altima Jerking Between 1st-2nd Gear

I have wrote on other forums and i was wondering if any of you have experienced the same problem I currently have. My car will sometimes jerk from 1st-2nd gear and its a automatic. I can tell when it's about to jerk because it seems like it is staying in first for too long. I took it to the repair shop and they said there was a corroded wire that was tricking the computer in it making it downshift when it was trying to go into 2nd or something like that. They fixed it, but it quickly came back and i took it in and they are now saying they aren't seeing the problem and today they said they are going to try again and discover the problem. Anyway does anyone have any idea what this could be caused by?