Land Rover Repair: range rover, range rover hse, gas mileage

Question
i have a 03 range rover hse and when i drive it it starts to shake or stutter my gas mileage have gotten bad, to me it feels like its shaking from the bottom. i have changed the sparks plugs and i still get the misfire code cylinder 4 and 5 changed the coils still nothing.

Answer
If you changed the coils, and changed the plugs, and still have misfires it is time to use a more sophisticated diagnostic system.  Find someone with the factory test gear or an Autologic - either the dealer or a well equipped independent specialist - and look at the live data.  You need to know if it's rich or lean when it misfires, and decide where to go from here.  There are certainly many possible causes of misfire, but you hit the most common ones.  So it's not obvious where to go from here without further testing.