I just finished changing my plugs on my 5.3, and now it misses under load. It does not miss when it is at idle just when it is under load (taking off from stop). I used the NGK TR 55s and reused the stock wires. And i gapped them to .055.

 

check the wire connectors. did you use di-electric grease? old wires are known for pulling apart.

 

You might have cracked the porcelain on one of the plugs during installation, accidentially slammed the gap shut while trying to put it in, may be a loose wire, or a wire got busted upon removal.

 

yes i would check all your plug wires sometimes they are hard to hear or feel, when they snap back on, but it could be any of the problems listed above.

 

Is it possible that the gap could be to open. Is it noticeable when the wires have been pullled apart. And i did not use di-electric grease.

 

I regaped all the plugs to 45 and changed all the wires. And still the same. Could it be possible that my truck does not like the ngks.

 

common problem with some of the ngk's is the connector that the wire clips onto becomes unscrewed and causes a late/weak spark causeing a bad miss

-Erik

 

I doubt that your truck doesn't like the NGK's...check the tips like negativeswitches mentioned, and inspect the plugs for any visual cracks. Do you know which cylinder is missing? If you narrow it down to one cylinder, you could try switching the plug with another cylinder and see if the miss moves with it. If not do the same process with that cylinder's spark plug wire...if the miss switches cylinders, you've found your problem. (you can narrow down which cylinder is missing by unplugging injectors while it's running...the cylinder with the least amount or no change to the idle is the cyl w/ the mis)

 

efi live can do a fuel inj. cyl balance test if you have or know someone that has

 

Could it be a coil pack?