Ok I got this truck from my mother-in-law for free with a blown head gasket cylinder 6 driver side. I did the replacement had the heads machined put it all back together by the book. Now I can't get it to fire on all 6 cylinders only 5 I think. Thought maybe bad gas (it sat since late November) put 5 gallons (over double the gas) fresh gas and half a bottle of b-12 chem tool. Dubble checked all plugs wires connections (coils plugs wires all new). I drove for about 10 miles oil pressure and temperature stayed perfect but no change in running truck shakes a lot and no real power. Don't sputter or backfire no engine codes other than imcr bank 2 open. Engine is 4.2l v-6 170k miles. Any ideas would be great thanks.

 

you can have a misfire, but not bad enough to set a code YET... sooner or later the code will appear... Or if you have a real time reader, you can see what is going on and diagnose it that way.

 

Sounds like the plug wire order you have is not correct.
A misfire for any reason should set a code.
On your ignition system it is a waisted spark type.
That means spark will be on two cylinders at the same time.
This may fool you into thinking its correct.
What actually happens is the spark to the mate cylinder must occur in that cylinder's exhaust cycles when it has no effect.
Otherwise every cylinder is monitored for rotation time when its time comes to provide power to the crank shaft.
If there is a problem the crank will not get the power and slows rotation time which is detected by the Crank sensor.
It will set a code when the time is too long.
Double check the plug wire order and get a Scanner and look for code set.
Also be sure the fuel injectors are plugged up in the correct order or you can have the same result.
Good luck..