1998 Ford Contour transmission slipping or jumping out of g

I have a 98 ford contour with approximatly 160,000 miles on it. About a month ago the o/d llight started blinking on and off and the car jumped a couple times as if trying to shift gears. But it stopped for awhile. However, now once it gets warmed it starts to act like it is slipping or jumping gears. At times it will stop if you keep driving but then starts again. We had the computer tested and replaced the maf sensor but it is still acting up. I am only the second owner of the vehicle and have not even had it for a year so I am unsure as to when the trasmission fluid and filter was changed last.