LS1 missing

[Jimr]

Have never posted but have followed for some time. I have a 68c10 and have added a 1999 Camaro LS1, 4L60E and kept the same wiring and computer. It has been programed but not when driving. I have one problem. It misses at idle or slow speeds from time to time. I moved a new fuel tank to under the bed, new outside fuel rail pump and filter, new fuel lines. I changed the injectors but thought the new ones might not be good so I cleaned the old ones and replaced them. Each time I change something I think its better but it starts again after a few miles. Could it be fuel rail dirt? How can you clean it? What other things could be a problem?