When going up hills the Auto (2001 GU) does not kick back to 3rd even if the accelerator is fully depressed. Taking my foot off the accelerator and then putting it down again, the auto will select 3rd hitting about 2500 RPM but always then changes to 4th about 2-3 seconds later. I have tried playing with O/D both on and off and also the A/T Hold Power Switch without success. Not sure what I need to check, Auto or ECU or something else?