noticed that GlennMC mentioned something about maybe being an electrical component after warming up. I am still having this problem with missing. Have had intake manifold gasket replaced as was cracked, some fluid in No6 cyl. replaced 02 sensors. at least 2 of them as the service iI went to said that it was showing on diag. that the 2 after the cat. where acting weird. took out egr and checked but was functioning ok not much of any build up. vacuum at egr seems to be working . don tknow if it is enough. any other electrical problems I should check? Appreciate all the help everyone has given so far. Am getting real tired of this problem. when dealers cant even help. Just want to charge for something that doesnt work.

 

This might sound dumb - but have you put good plugs and wires on your truck? I had plugs go bad in only a few months.....try jacketing your wires with rubber hose too - make sure there is no spark jump to the block. and coat all of the contacting surfaces with di-electric grease.....

Robbie