3 times today my TR jumped out of 5th gear with the cruise control on, on a flat peice of highway, WHY? the box was replaced 20,000km ago, and no matter what I do with the throttle, ie chop and reaply agressivly at 100km/h i cant make it jump out. Whats going on.
the car is a TR SE, 2.6l, manual (obviosly) with 267,000km on the clock.

mabi wrong oil

Gearbox/engine mouns may be the problem.

gday
was your clutch kit replaced with the gearbox? you might find its a weak pressure plate

Replaced with new or replaced with junkyard parts?

My TR kept jumping out of 5th gear, discovered that 5th gear syncro was faulty. After this was fixed it no longer jumps out of 5th gear...

turns out ive got two broken engine mounts. must have done it last friday night on a flat stic cruise