727 Shifts Down to 2nd at highway speeds

Yeah, something's not copacetic there.
It looks like you have the lever adapter on there, but the throttle stud is pinched on the edge of the lever instead of going through the mounting hole.
Besides being unsafe, that's goofing up your geometry. It needs to get assembled properly and the kickdown readjusted, then see where you stand as far as it slipping in and out of kickdown.
In the pic below, the kickdown linkage is slightly different because of the year and application, but should give you an idea of how the throttle stud mounts to the linkage. (Pardon the grody kickdown linkage, it was a trial fit and alignment before cleaning, painting and final install.)