Slight knock when accelerating

Hi. I recently bought a K1500 Chevrolet Suburban that has about 88K on it. When I acellerate SOMETIMES it has a slight knock. It seems as if it cannot get enough gas. Does this sound like fuel injector problems?? Spark plugs?? I recently bought some fuel injector cleaner and plan to put this in at next fill up. Any other suggestions or help would be greatly appreciated.
Also how often should spark plugs be changed?? The OEM's are double platinum but I am unsure how often/if they should be changed. Thanks again for any help.

K1500

I had a very similar post to yours, mine was titled "slight knock/ping during acceleration" and I got an informative reply from "99ssconv". Rather that duplicate all that text here, I'll refer you to to the reply to mine. Seems like the same deal (on the list of threads it about 4 items above yours on the page). Good luck...