Engine hesitation while in park 2004 Sport Trac

I have a 2004 Sport Trac. When I started it yesterday I noticed a hesitation when I stepped on the gas while the vehicle was in park. The RPM guage would not go over 3000 RPM's even when I had the gas pedal pressed all the way to the floor, and it wasn't smooth when I stepped on the gas, it was kinda jerky. I let the vehicle warm up and took it out on the highway and it ran fine. I even got the RPM's well over 5000 a couple of times. When I returned home and put it in park it was still happening. The day before I did fill up my tank from a gas station that I normally have not used in quite some time and I'm wondering if I got some bad gas? My vehicle only has 12000 miles on it and I plan to take it to the dealer but I would like to have some clue of what is going on before I brought it to them. Any and all help will be appreciated. If anyone needs more information please contact me. Thx.