You can check first sleeves and synchors. It is possible worn gear engagement teeth. Take a look at it.Hi I’m new to this forum. I have a crunch going from 3rd to 4th gear at high revs. I think it could be the synchros that are going has any one got any more info. There is best pex crimping tool review at AutoGuysLand. If you want, you can access it. Also is it worth a rebuild or getting a new gear box ?