Try to have the accelerator or throttle position sensor checked and adjusted. Automatic transmission usually uses the signal from this together with the speed sensor to know when to change gears. If set too low will make your engine to shift late. If set too high will make your transmission shift early. What is your ride ba? When you try to full pedal the accelerator cable your AT will kick down (usually used in overtaking).

The throttle position sensor is located where the injection pump. It moves and its position depends on the accelerator pedal. Usually three wires ito. When adjusting have a mark so you can return it to original position if no improvement. A voltage tester will be very handy in adjusting this.

Hope this helps.