several way to check the fault, first is make proper adjustments on the kick down cable then check for correct pressure on the vacuum regulator underneath the transmission (there is a color code for each individual tranny) even if you have the same year and model, the vacuum box may be different. if that don't work then you need to find out if your fluids are on the right level as well as your torque converter fluid level. if that does not woek then you need to have your tranny taken down for servicing. may have been the velve body.