03 Hyundai Accent automatic transmission problems?

My 03 Accent has 125k miles on it and just started having problems shifting gears. It has a hard time in reverse, but is fine in 1st. It lurches pretty hard when shifting up, but once on the highway it does fine. When slowing down, it lurches and shifts back and forth into low/high gears. What can I do, or what should I check. The transmission fluid is fine as is the engine oil.