727 not hitting second hard enough

I doubt if the KD rod is causing your soft shift. One of the downsides to the TF design is the non-sequential shift action that GM transmissions have. For the 2-3 shift in the TF, a band has to disengage & a clutch has to apply. This timing is critical. Shift kits do not fix worn out transmissions. If the front clutch[ 3rd gear ] plates are worn, I could see a soft[er] shift occurring. Is the pressure reg spring correctly adjusted?