This procedure will ensure that the transaxle will kick-down (down shift) at the appropriate throttle position which is approximately 90% throttle (90% TPS). A means by which you can fully depress the throttle pedal fully is required for this procedure, either a tool or a friend (who is not a tool).
1) Disconnect throttle linkage between transaxle and throttle body (TB) at the transaxle
2) Adjust cable between throttle pedal and kick-down lever on trans such that both reach max at the same point
3) Hook up throttle linkage between transaxle and throttle body.
4) With throttle pedal and kick down lever at max, adjust linkage at throttle body such that the TB reaches 100% (WOT) at same point where throttle pedal and kick down lever reach maximum
How to make adjustments on the throttle cable and linkage are fairly self-explanatory, refer to your Bentley repair manual for details if/as needed.