Grabbed a set of cables out of the local pick n pull yesterday and put them in today and here's what I found...

When I pulled the old cables out I fixed the bracket that holds them so it won't move anymore. Threw the new cables in and was about to put the battery back in when I realized since I took the big U-shaped bracket out and never put it back in the tray was sagging enough to make contact with the shift cable.

What I'm thinking is that while I was messing with the speed sensor, battery in and out a few times, once the tray started sagging enough to make contact, it keeps it from fully engaging 5th gear. So, everytime I try to accelerate while in 5th, the engine rocks backward just enough to where the tray pushes the lever out just enough to pop it out of gear.

I'm going to test it as soon as I get a piece of thick flat steel to use as a support and see what happens. Wish me luck.