02 Denali Idle surge and spark knock? at startup

I have a 02 denali 6.0. First problem is it will surge at idle and the rpms vary a few hundred rpms. also, the interior lights will dim and brighten as this happens. It does not do this surge all the time. It will surge and about 10-20 seconds later idles fine. It mostly occurs at startup. My second problem is when the engine is first started, i hear a knock. It does not rattle or knock for any period of time. Just a millisecond when the engine fires up. Sort of sound like a spark knock. Any suggestions?