Isuzu 6spd amt gear box plays up changing 2nd to 3rd but not all the time

well that one came from left base shall check well that one came from left base shall check

2nd to 3rd gear selection is the gear lever /selector pulling 2nd gear back to neutral and then selecting 3 rd gear rail and moving that gear
the clunk could be the rail not moving properly into the neutral position before the 3rd gear rail is moved
now why I suggested mounts is that the shifter adjustment unless the stick goes directly into the top of the box ( cable . linkage etc ) may be affected by a loose box mounting
next the suggest may be that when the selection is made the torque reaction may be moving the gear train and the clunk is outside the box
if the lever is direct into the top of the box then the pivot pin that the lever moves on may be loose and not affecting a proper change
Box problems is the last thing I would suggest unless you have metal particles in the gear oil
much unnecessary work is done when a pre investigation will reveal the problem and save time and money 2nd to 3rd gear selection is the gear lever /selector pulling 2nd gear back to neutral and then selecting 3 rd gear rail and moving that gear the clunk could be the rail not moving properly into the neutral position before the 3rd gear rail is moved now why I suggested mounts is that the shifter adjustment unless the stick goes directly into the top of the box ( cable . linkage etc ) may be affected by a loose box mounting next the suggest may be that when the selection is made the torque reaction may be moving the gear train and the clunk is outside the box if the lever is direct into the top of the box then the pivot pin that the lever moves on may be loose and not affecting a proper change Box problems is the last thing I would suggest unless you have metal particles in the gear oil much unnecessary work is done when a pre investigation will reveal the problem and save time and money