Shifts out of H when going downhill or use exccesive engine brake

[Virandy Lurker Find all posts View Profile Close Virandy]

Hello , I have a 2007 Prado , 5 speed automatic , diesel 3.0 engine 1KD-FTV with 450.000km. After searching a few hours here and not finding my problem i ask you kindly to suggest what could be the reason that my car's gearbox little lever slips out of H into N when i use the engine brake in downhill situations . To resolve this problem without stopping i put the big lever from D in N , put the small lever fron N to H and at last the big lever into D. If i use the foot brake more then there is no problem , also when going on level ground there is no problem unless i use exccesive engine brake intentionaly.