Wrong pinion angle causes driveshaft vibration, that will cause the trans to fall out of gear on a slight down grade where there is little pressure on the gears. My car is far from a stock deal, a lot higher springs on the rear than stock, hence the pinion angle problem. As I said before I have about 5000 miles on the 855 and it works great. Also I very much doubt you could ever get a better guy than Jamie to work with.
Just Sayin, and I had a new 67 GTX when I was 20 years old, so have been around the block a couple of times