4-speed A/T but acts like 5-speed, how?
I just bought a '05 Kia Spectra 2.0L A/T (no OD button) about a month ago. It has that usual A/T shifting setup, D,3,2,L. When I was going up hill at about 50 mph at about 2000 rpm in D, the engine speed increased to about 2250~2300 rpm as the hill got little steeper. Initially I thought it went into 3rd gear to keep at 50 mph. The hill became even more steeper and I felt the vehicle speed was going to drop. So, I shifted down from D to 3 but did not really expect to the engine speed to change (since I it just downshifted to 3rd gear by itself). But it did again. The rpm increased to about ~2600 in 3rd at 50 mph. Just to experiment, I shifted to 2 position, then the rpm shot up to like something ~3500 rpm or little higher, but less than 4K. I immediately shifted back up to 3rd.
The very similar thing is noticed on my 2001 Dakota 4.7L V8 A/T. It is a 4-speed A/T. When I drive in D position and when there is an increase in load (ie. hill), the rpm rises by a few hundred. When I turn off O/D (4th -> 3rd), the rpm rises again once more by a small amount. I go up the same hill everyday and I repeatedly did this experiment and I see the same thing happening over and over. This makes me really curious about how the A/T works. I have had many other A/T cars before and have never noticed anything like this.
When I asked a dealer service dept about this, they didn't really give me clear response. They said something like the trans uses existing gears to create another gear ratio between 4th and 3rd for smoother transition - I don't know if that's true or not but that's how I understood.
Can anyone explain what is really happening?