Flickering

The interior lights and head lights are starting to flicker on my 2003 chevy cavalier. At times the seem to flicker slow and at other times they flicker at a slower pace. I have noticed when they flicker at a faster rate that my car starts to surge when I am going down the road. Some times it does it when I am stopped and sometimes they don't. I have also noticed that it is also affecting my gas mileage since it has been surging. Also I have noticed that my air conditioner is also effected by this to. It has almost 296000 miles on it. I have just recently replaced the alternator on it. Other then that I have done nothing to the car out side of plugs and trying to keep the oil changed. I have checked the connections on the alternator and they look good to me. The batteries cables are clean and look like they are in good shape. I have to get up early for work and drive about 55 mile to work so am worried about breaking down. So any help would be greatly appreciated. Thank you very much for any help with this problem.