pops out of 5 th gear on 1993 Toyota Corolla

only pops out of 5 th gear a couple of times and then will stay for 30 or 40 mile and then pop out again, its done it well drive a constent speed

Asked by for the 1993 Toyota Corolla
Most likely to be a internal gear box problem where the synchro hub and outer sliding hub haven't enough tension to stay engaged. Check that the linkage allows full engagement (its not sloppy and worn).
i will check the linkage