my nissan almira pulse 2003 reg is jumping out of fifth gear ?

is there any thing I can do,? when revving up a little on slight hills after driving for ten minutes or so the fifth gear jumps out, it is ok if I hold the gear knob and I don't feel to much movement, could it be the engine mountings are a bit loose or the linkage needs looking at had the tracking done a few days ago as some one hit the front wheel on the drivers side in a near miss any ideas ? thanks