1998 GMC Pickup,PO306

My 98 5.7 litre p/u had a trouble code of PO306 come up after I scanned it. I no that this means misfire on #6 Cylinder. I tuned up the truck and scanned it again after the dash light came on again. The Same code came up (PO306). I sent the truck in to have the injectors flushed but this didn,t cure the PO306 problem. Through process of elimination I replaced #6 fuel injector and nozzle assemble but the code still comes up. I,m stumped at this point and considering removing of the main intake manifold and search for possible vaccum leaks or possible a bad lifter. Does anyone else on the forum have any further ideas what the problem could be or does this code refer to more than just #6 cylinder misfire?

I'm going to move your post to the Chevrolet C/K forum here's the link:

http://www.automotiveforums.com/vbulletin/showthread.php?t=379456