What's your fuel delivery setup? I think ls1 fuel rails should be preset to 58 psi, at that psi ls1 car injectors should be 28 lb per hour. If your pcm is tuned for a truck it could be set at 24 lb per hour injectors making it rich. If you can I'd verify fuel pressure, check for misfires, and pull those injectors out and get them cleaned. You should be able to see the gunk on them if theyre blocked.