I have had an unusual problem which I found hard to understand.
When selecting 1st gear, it felt like the gearstick was not going far enough forward, and when driving along in 5th, it would occasionally jump out, into neutral.
The gear stick was vertical in neutral, so I had no reason to think the selector rod was at fault. It felt like it was about 1/4" too short, but the roll pins on the centre UJ were firmly in place, so I had no reason to doubt the rod was the right length.
It felt like the whole linkage was hitting something, and not going far enough back.
So I left the car in 1st gear, and looked closely at the whole rod linkage. Where the rod passes the exhaust manifold (header) it was hitting the manifold, so I had to move the UJ away from the manifold by adjusting the connection to the bracket where it attaches to the bellhousing.
I loosened the 3/4" nut and turned the bracket away from the rose joint as far as possible, but still the clearance was not enough. As I turned the bracket on the threaded rose joint, I noticed the bracket is slightly angled, so I turned it back 180' (half a turn) and the linkage was clear of the manifold. I had not realised before that the bracket (which is held to the bellhousing by the long 1/4" bolt with the 7/16" head) has a right and wrong way round to fit it.
We learn more all the time.