I have been having a problem with my truck. It starts up fine. However, about six months ago I noticed a loud wistling/squeeling sound comming from my distributor cap. But it drove fine. Now the truck is jerking like its misfiring or somthing. Its acting like i bougt bad gas. When the motor has warmed up or driven a bit the whistle goes away and it seems fine. Can this be resolved by changing the wires cap and rotor etc...? Where do I start?.