2001 Mitsubishi Galant What is wrong with my car

Engine Performance problem
2001 Mitsubishi Galant 4 cyl Automatic 166,00 miles

I recently bought my car and now all of a sudden it doesnt want to get the pick up it used to have when I first bought it. I have been told it could be anything from my transmission, catalytic converter, to a fuel pump. The thing that my car is doing is... I start my car up it squeals a little bit and it has this slight putt-putt noise to it, it also has the same noise when I am at a stop. When I go to give it gas it takes it a little bit to kick in...after a few seconds it does. Can someone please give me a almost definate solution to what the problem is? Feel free to ask more questions if you think that will help.