I had the codes read on my 2001 Silverado 4x4 5.3L vortec. It was having power problems. Came up with a p0300 and o2 sensor. I replaced 02 sensor. Still had the p0300. Changed the fuel filter and no help. Took to a local mechanic. He ran it on his diagnostic computer. 2,4,6 and 8 cylinders are randomly misfiring. He checked the compression, its good on all cylinders. Changed sparkplugs, wires, coil packs, EGR valve and intake gaskets and the plugs are not fouling out either. Ran it on the diagnostics computer and checked the computer and all sensors. Everything is working. Basically, he ahs thrown parts at it, and not been able to fix it. He wants to take the ehads off nowand check the valves and the Head gaskets. Anyone ever heard of this? Also, cylinders 1.3.5 and 7 are fine. No problems.

 

Take it to someone else. He does not know what he is doing. Do not let him tear your engine apart. What is the fuel pressure? Has he used a scope to check the crank sensor pattern? (probably not).

 

Would that make only one bank misfire and the other side have ni problems?

 

check back pressure before convertor on that bank it is most likely plugged also was the o2 sensor the preconvertor one on that side

 

do yourself a favor and find yourself a new mechanic.
sorry i didn't realize how old this tread was. you already probably fix the problem or scraped it by now. my bad!