The truck is is cranking longer than it used to....especally when hot(used to start on 1 or 2 turns..now it's 10 or 12)...it still starts right up, but not as quick as it used to. I have checked all the return fuel lines and there are no leaks at all.....could this be an indication of a dirty fuel filter ????? How do ya know when it's time to change the fuel filter ??? Any info/idea's would be appreciated, thank you, CD