Reduced engine power

About a month ago the reduced engine power light came on and I couldn't drive over 15 mph. Before that happened my car was cutting back on speed and cutting off when I would stop at a light or slowed down almost stopping. I know that I need 2 sensors but the guy at AutoZone said that those sensors wouldn't make the engine reduce power. I'm a woman so I don't know much about cars so I am trying to find some advice so that when I take it in to be fixed I won't feel like I'm being taken advantage of by someone telling me that I need more done than I actually do. My car has also had a lot of modifications done by the previous owner and I think that it was used to race at some point. Any advice will surely be helpful and appreciated. Thank you.