Nissan Repair: Nissan Serena 1995 diesel 4 w/d auto transmission, recod, auto transmission

Question
Hi rob.
I have gone thru 3 transmission replacements in less than 2 000 km ( must be a recod?) and they are all failing the same way. At speed the van down shifts and eventually smashes some of the gears ( reverse gear as well). The replacements have been done by 3 different specialists. The last replacement included replacement of the oil cooling rediator, and throatle position sensor and in less than a week and 950km later, from start it did not change gear from first to second. When I let go on the accel, it then changed and immidiately changed back to first. I have stopped using it and am now wondering what next- Please help. I have spend  so much money on specialists.  

Answer
why are you coming at me with negative comments, you asked for my opinion on what i think you should do , i told you.  obviously you like taking this vehicle to people that dont know what they are doing and i told you to find somebody else...i think thats more than a fair enough answer.  do you want me to tell you grab some wrenches and ill stay on instant messenger and show you step by step how to start rebuilding your entire car?  this is a free site and i do this voluntarily, if you dont care for the answer then keep taking your transmission to unqualified mechanics.   have a nice day.