i get valve clatter in my truck at highway speed and approach a hill. I normallyturn off my o/d and it will stop and go on . i was thinking my timing may be off a littlebut it idle good. and my gas mileage sucks . i need help any body got a suggestion

 

run some seafoam thru it... see if that helps ... a good oil flush cant hurt either

 

You might even want to try a higher octane fuel if you use reg try mid grade.