This is a VERY general type of problem...It could be any of these things...A routine ignition system tuneup usually fixes this problem, though..Look at the plugs, the center electrode should be squared off, and not round looking on the edges..
Other possibilities are:
Fuel injection system malfunctioning...How long has it been on the fuel filter? Any chance of getting bad gas?
Faulty coil pack...Is the engine light on?
Brakes binding....This is more common, than not.
Low transmission fluid level. This places extra strain in the trans, and friction is slowing the car down...
There could also be an emmission system malfunction....Again, is the engine light on?
And lastly, there could be low or uneven cylinder compression....A compression test (with the guage) will have to be performed on the entire engine.