I'm not sure if this is cause to worry or not, but there is a bit of back story to this as well;
I drive a 2006 Toyota Corolla with an automatic transmission. About 3 years ago, a line in my transmission had degraded and leaked all the fluid out. I drove the car for about 2 hours without realizing this, until finally getting to my destination and having the car not get in gear. The repair was completed successfully, and the shop claimed there was no damage. Lethal bullet dodged.
Since then, I have not noticed any strange transmission issues, except for in the past few months. Occasionally, a part of my commute for work requires me to drive on a road with quite a steep downhill bit, tractor-trailer warning signs and all.
The hill down has a 45mph speed limit. I will notice from time to time that while braking down the hill, my car stays at a higher gear, or will even shift up to another gear. This causes the car and pedals to vibrate quite a bit. Once I'm at the bottom of the hill, the speed becomes 55 again, and usually once I get back on the accelerator, the transmission will shift down properly.
Is this something to be concerned with? I only experience it on hills like this, but that example was the most clear.