Fifth Gear Jumping Out

[foxyboy]

hi bit of a long one,my avensis t4 diesel is jumping out of fifth gear i can feel movement if i hold gear knob,it has had the gearbox reconned in march,and when problem started garage said rear engine mounting was kaput so bougth new one which was fitted still had same problem so they then fitted front engine mount,still got the problem,warranty ran out on gearbox 12/6/12,before i go spending more has anybody got any ideas or had this problem and solved it,my trust in garages is very low.

thanks for any respones.