Does Shifting Fast Hurt the Transmission?

Shifting too quickly while your car is still in motion can cause significant damage in the transmission because there is a spinning coupling mechanism that can prematurely fail if it becomes worn from the harsh gear change. Always come to a complete stop before shifting into another gear.

Does shifting an automatic hurt the transmission?

But the good news is that it doesn't do any harm. Unlike a manual transmission, which forces you to use up a little bit of your clutch disk every time you shift, an automatic transmission uses a fluid to transmit power from the engine to the driveshaft.

Should I change gears fast or slow?

The basic rule is that you change up through the gears as the speed of the car increases and down when you need more power from the engine. For example, you would change down to a lower gear when climbing a hill or pulling away at low speed.