If I can hijack this for a moment...
I too am experiencing an issue with a shift point that I believe is too early. It is a rebuilt, zero miles, Torque Command (AMC) 727 with a transgo shift kit.
I have what resembles the Mopart multi-segment throttle pressure linkage.
There's is about 1/3" of slack in the carburetor link bar before the throttle will start pulling forward on the throttle rod.
I got this much slack by pulling all the way forward on the throttle rod, and opening the carburetor linkage to full throttle and tightening down the nut on the carburetor link bar.
Since the shift seems too early to me, can I just add a little more slack in the carburetor link bar so that maybe 3/4" of throttle travel will occur before pulling forward on the throttle rod?

Thanks!

Steve