Back to the workbench!
We determined that the motion of the linkage that moves to reverse/5th was limited. Why?
Ah hah! The spring and plastic limiter that keeps you from selecting 6th and 7th gears was installed wrong! A
The linkage resorted, we reassembled the transmission for the last time. We were sure to use plenty of assembly lube to make sure things went together well.
We properly torqued all the fasteners...
And tossed it back in the car. We've gotten really fast at this.
Where... IT WORKED! WE FIXED IT!!! And it cost absolutely nothing!