What is the cause of disengaging transmission and if there are possible diagnosis to check and fix it aside from having it repaired in a shop for a very expensive cost?

 

edited..

 

Can you supply a 'bit' more info. like miles on the trans, when it disengages or stalls, speed it occurs like on a launch/cruise ect. or noise/s, anything to help refine a request.. Or as well as any driveability issues before the problem if any.. OD light flashing? All gears affected?