My 09 Yaris feels a bit off

[MRxAmazing]

I've been noticing some issues with my car accelerating and decelerating. But more so the acceleration. There are times that I step on the gas and the car accelerates quite a bit more slowly then I feel it should. Like I have the pedal down, but it feels very sluggish. And then other times I step down on the gas (lightly) and it takes off. Almost like it's jerking forward.

On the opposite side of that, I've noticed the car slightly less than smoothly decelerate when I'm not on the gas. I even tested it going down a steep hill (doing about 50 approaching the top). The car didn't gain any speed going down (I'd usually gain at least 5-10 mph in my old car).

For the accelerating issue, I was thinking it could be a spark plug, ignition coil or (hopefully not) transmission issue.

As for the decelerating, I was thinking it could be a possible brake issue. My Sable had a problem where my calipers would expand when they heated up causing my car to brake without ever stepping on the brake.

Any opinions?