Chevrolet Repair: fuel injection, mech shop, chevy tahoe

Question
About a year ago i had a real bad misfire problem. So I tore down the motor had the heads rebuilt replaced all the popit valves all new gaskets. I put it back together got it fired up  wasnt running right took it to a local mech. shop and had them do the timimg on my engine after they where done they told me that it still wasnt running right but wasnt putting out any codes. I took the truck home parked it and left it alone for the winter. I had to put a new battery in it well when i did that started the truck and it ran like a champ no sputering nothing ran awsome. So none the less ive been driving it for about a year now and all the sudden its slowly started running crappy again so I pulled all the pluggs and 5 out of the 8 plugs had some kind of corrsion type build up on the ends of the plugs. I heard from someone that the problem is the egr valve. That it would be causing the misfire. My truck is a 1997 chevy tahoe 5.7 vortec. Please help if at all possible thank you matt

Answer
Hey,

 Corrosion on the plugs?  Like a whitish or blackish buildup?  Could be oil intrusion from the valve guides, head gasket, excessive EGR functioning.  Send me a pic of the plugs and I will tell youwhat it is thats building up and try to help.

w