2000 Chevy Impala OBD2 Codes and misfiring

I have a 2000 Chevrolet Impala with the 3.8L engine. This car has been such a nuisance for me. I recently had two different codes that showed on the pcm. P0171 which is my fuel is too lean and P0306 which is a cylinder misfire in cylinder #6. I have replaced my vacuum lines, replaced my Mass Air Flow Sensor, Replaced spark plugs and wires. The car, when parked or at a stop sign would continually jerk forward and back very hard at first. Once I changed the vacuum lines the problem has seemed to dissapate some. I still have a light jerking but now it will do it on the highway during high or low speads. My check engine light is constantly flashing telling me that the car is misfiring. I have talked to several mechanics and everyone I talk to has a different answer. Can someone please help me with this problem. I did throw two different EGR codes as well after replacing the vacuum lines but have since gone away within 30 miles of driving. I am totally lost on this and have already put a lot of money into the car, so much that I dont want to get rid of the car but I know not what else to do.