I have a 2002 GMC Yukon 2wd 5.3 Liter. It has approximately 80,000. Lately, I have had what seems like fuel pick-up problems at start up only. From new until recently, the car would easily turn on simply by turning the key without having to step on the gas. Now I have too turn the key at least twice before it will turn on. Even when I press on the gas pedal, it still takes a few seconds for it to start. I've changed the spark plugs, had the fuel system, including the fuel injectors cleaned at a service shop. The vehicle runs fine, it's only this particular issue at start up, that's got me puzzled.