Why does my car shift gears when i release the gas pedal?

I have a 2002 Ford Focus ZTS, Automatic, 16 valve, DOHC.

My car takes forever to change gears from 1st to 2nd. It used to change smoothly at 15mph but now even if I LET GO of the gas pedal it keeps accelerating until it changes gears, and when it does, the car gives a semi-hard kick. This is only for the 1st shift. After going into 2nd gear, I hit the 25mph mark and if I LET GO of the gas pedal, the car CHANGES gears and gives a little kick. If I DON';T let go of the gas pedal the RPM will go up to 3,000 and then shift gears. I feel like it wastes a lot of gas like that. The rest of the gears are the same at 35mph and 45mph. It almost makes me feel like i'm driving a manual(standard) car when it's an automatic. What do you think it is? Please help. How do I fix it?Why does my car shift gears when i release the gas pedal?
Bring it to a mechanic, probably it has a problem in transmission already.