heres the story, i dont drive it very hard, i commute 110 miles a day to work. truck started smoking heavy greyish and was knocking around 2000 rpm at cruising speed, when the engine was warm. with the engine cold it wouldn't knock and ran ok other then smoking. i took it in to one dealer to have injectors tested and they said it had blown head gaskets and the injectors were "fine". I did NOT believe it had a blown head gasket because it had no symptoms of that, went to another dealer and had injectors tested and 7 of the 8 had high balance rates and after they cleared the codes and did whatever they did to test it made it run rough all the time but no knocking on the way home. so i bought 8 reman injectors and installed them, got it back together fired up and still runs rough, like running on 7, with light smoke. I scratched my head for a bit and went out into the shop and noticed that 7 of the 8 injectors i took out had the washers still on them and cyl 6 injector does not, (which is the cyl with no compression) and i do not remember the washer falling off the injector on the way to the bench nor did i hear it drop off. I know for a fact i installed 4 new washers on the drivers side so i may have 2 on cyl 6 injector but i dont think this would be my problem since the injector should still be seated on the washers to seal, maybe im wrong. so i took the truck to a shop that the owner/mechanic use to work for GM for 20 years or longer and he plugger in the tech 2 and cyl 6 balance rate was +15, cyl 3 was 0.3, and the rest were -7. he pulled cyl 6 glow plug which the tip was like melted off he said and did compression check and nothing, and this is where i am at.