1996 geo tracker think I need a new transmission???

I have a 4 door 1996 automatic geo tracker. Some times it runs like a dream, but more often than not when I go for the stoping possition it will sometimes stall or have a problem shifting. It will Idle up and down and make quiet a bit of noise If you push on the gas it will some times stop but usually it will stop once you get up to 25 miles an hour. I am thinking that I need a new transmission, but could it be something else. I just want to be informed before I go to a mechanic. It was just serviced and passed inspection a month ago. Also sometimes when I start the car the engine light is on as well as the o/d off light. Sometimes the o/d off light will flash but then other times neither of them are lit. An information will be great. And estimated costs would be helpful as well. Thank you ahead of time!!!