Do I have to change the distributor cap on the 4.3L? Is there actually a distributor cap or does this engine have coil packs ? There is no mention of replacement at the GM service site , it only mentions spark plugs at 150,000 km.

Yes there is a distributor cap on your truck, its between the rear of the engine and the firewall....

If you are going to do the plugs you might as well do it all at once. Plugs, Wires, Cap & Rotor. Just to save a headache later.

I can see the item that looks almost like a distributer cap but it is not the tradional shape. I did a search on the net but there are no listings for a cap and rotor for the 2006 Blazer 4.3l engine.
http://rep.racepages.com/parts/racepages/parts.jsp?year=2005&make=CV&model=BLAZ-2{embeddash}DOOR-004&category=F&showChildren=False&showdc=true

You won't need one yet, it should be the same as the 2004 and 2005.

I don't think they changed anything when they went to 06.