Jeff's 727 rebuild thread
Just remembered this is the trans that D55Dave pointed out, during your disassembly, he suspected someone may have previously installed a shift kit. If your kit had you shorten a valve, and someone else had done that same mod before, that valve could likely be allowing incorrect fluid flow now. Same is true for valve body casting mods. These issues would definitely cause the issues that KickDown detailed in his posts. Also, I forgot you are using an aftermarket kickdown cable, not the linkage.