[cmfml]

I have an 04 impala 3.8 police package that was having the same problem with missfiring when accelerating hard or going over 55 - 60 mph. I changed the plugs and wires with no change. Then I had a friend in the automotive business hook up a professional code reader to it while driving. It returned the missfire code and furter indicated that it was plugs 3and 6 that were missfiring. Since wires and plugs were known to be good my friend tested the ignition coil and found that the coil for 5 and 6 were not firing at the right voltage causing a verry weak spark. Changed all 3 coils just to be safe and now it runs perfectly. Coils were fairly cheap arround 35 a piece and a sinch to replace. Note be carefull testing the coils your self they are very powerful and will give you quite a shock you wont soon forget. As for the fan problem check your relays located right above the battery in a black fuse box. Getting your car read by a code reader would probably help identify these problems.