Help me please I'm wasting money on everthing

I have a 97 nissian altima it has 173,000 on it. The problem is when i'm driving it will want to shut off or when I come to a red light it will feel like it wants to shut off and then does but it starts right back up it doesn't do it all the time. I took it to the shop they put it on the computer and the only thing that comes up is a transmisson code. I have changed the plugs wires distributor I have no clue what it is please help I wasted a lot of money. The car runs great no other problems with but this one thing. Sorry forgot to tell you its a automaticand 4 cylinder