Tim the injectors cycling and this knocking are 2 totally different noises.GM has redesigned the 5300 for 2001 and no longer has the problem-but that does little to help the 99 and 2000's that are affected by it.I use Sea-foam engine treatment,it is only avallable at Napa stores,they have the exclusive to it,you pour in the intake while its running,stall it right out with it,let it set 5 minutes,fire it up.Man ,what a smoke cloud,you will clear the area out in no time.I did this a couple times and my truck runs better now-at least it seems to.My brother has a Caddy that had a carbon problem,the Caddy dealer said to use the sea-foam over the GM cyl cleaner.