Honda Fit Sport 2011 - Acceleration Problem

[TVel4]

Hello,

I'm not very car savvy so I will try to explain my problem as best I can...
I bought a new Honda Fit about 2 years about (2011)-- the car has just over 40,000 miles on it now. (long commute.) I had recently brought it in to get an oil change at my dealership and upon getting it back I noticed that the car was driving strangely-- being used to having a smooth ride, the car's acceleration felt clunky, almost as if I were lunging into gear when I applied pressure to the accelerator. If I would remove my foot, the deceleration felt odd too-- like it was pulling itself to a slow stop, instead of smoothly decelerating on it's own. I've brought it into the dealership three times now to check on this problem but they keep telling me the car feels fine. "feels like a Honda fit should feel" - but that doesn't make it feel any better for me. I even drove around with a tech a few times. I had my transmission fluid and air filters replaced, and the oil is new. I've also tried a fuel injector cleaner, but-- no luck. It bewilders me because it feels entirely different from how it did before-- the drive is not comfortable and feels to be shifting roughly- like I'm forcing it more and the drive just feels a more rough and bumpy. The dealer said the only thing they probably needs replacing are my tires soon-- would that play a part into my uncomfortable drive? It feels like a shifting problem but I don't have much knowledge in cars so it's hard for me to say exactly.

Any advice? I'm at a loss and don't know what to do-- thanks so much for any tips!