I have a 77 4X4 with a transplanted 460. It has a Motorcraft 4bbl made by Holley. The shifting lever that goes from the carburetor to the transmission is not hooked up. The truck shifts into 2nd at 10-15 mph and into 3rd at about 25 mph. I believe the shift lever can fix my shifting issues but don't know how to connect it.

 

No, it won't fix your shifting problems (I'm assuming we're talking about a C6).
On a C6, the kickdown rod is just that, for kickdown to passing gear when you floor it, that's it's only function.
The first thing I would do is check the vacuum modulator and its line. If that checks out okay, my second guess would be the governor assy in the tailshaft of the transmission.

EDIT:
When a vacuum modulator fails, it usually has symptoms the exact opposite of yours, not wanting to shift to second until around 60 MPH and not shifting to third. If the modulator is stuck or frozen, it could display the symptoms you have. I would pull the modulator (one bolt) and visually check to make sure the pin moves freely.