I have been fighting this problem for days and i just cant seem to think what could be causing it

I gave the car to the dealership to have them check for any codes and i was told that they found NO codes.

So the problem is the car doesnt want to get up to speed properly when i press the gas pedal normaly but if i just slightly press it down, the car gets up to speed nice and smooth. So i'm thinking this could be a fuel or tranny problem? (BTW the shift lever moves smoothly and gears shift up and down nicely too)

I''m sure the engine runs fine because i can get it up to speed no problem but in order to do this i just have to slightly press the gas pedal. If i floor it the car revs really high but doesnt pick up speed quickly like it should. I just don't want to go out buying things and finding out that the problem isnt this and that etc..

Any input on would be awesome guys. Thanks again