I made the same observation a while ago. I really wanted to see the pistons shoot out of the roof or smoke billowing from the engine compartment haha.

And... I thought there was a mode when this didn't happen, like it was while in a race or something when it wouldn't keep shifting, but it could just be my imagination. However, the cars top out while playing Cops and Robbers, even when you don't have the gold, so thar might be the mode I was thinking of.