Stalling engine while in drive position, what can i fix for this problem?

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I have done a little research and found no solution. My van started to stall while i drove it between 5-30 mph now and then (I took it to a service department and they could not find out what the problem could be at this time); after a couple of weeks then it just wouldn't drive anymore (I am trying to prevent making a huge payment on it to get it fixed and i would rather do it myself if i can.) I am able to start it then run it in park, mutual and reverse but when i place the automatic stick into drive the engine shuts off completely. I changed the "Throttle Position Sensor". And I put in drive and it iddled then i shut it off and started it up again but when i put it into drive position it didn't work/iddle again and just shut down again and again. Please give me any advice that can help my situation?