It may be coincidence that my manual trans needed
to rebuilt after I made several trips from Mammoth
Lakes to Bishop Ca. There is at least a 2000 ft.
change in altitude and I left it in neutral going down
over 40 miles figuring the engine was happier.
This was in a Ford and it was a used car, but
the shop that rebuilt it said not to coast in neutral
and explained what johngray just did about the
gears not turning, and hence lack of splash lube
to the bearings. The bearings were ruined.