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The EGR was used for lowering combustion chamber temperatures by diluting the intake air with spent combustion gases (for the purpose of avoiding creating NOx combustion by-product)... this also has the side-effect of dirtying up your intake manifold... yech.
GM has long since figured out how to lower CC temps (and NOx) by other means (timing and fuell).
If your annual vehicle emissions inspection does not force you to have it, then delete is as Doc said.
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I figured their abandoning had a lot to do with the way cam profiles are now vs where they were with my old ass trucks. That and much faster, more responsive processors and more adaptable OSs. My truck came with similar cam duration to the LM7 (which I believe still had EGR), but sat on a 111 LSA and used a 106 ICL. That builds a lot more cylinder pressure than the ~115 LSA of the LM7 and what may have been an ICL later than 115. Add variable cam timing to the mix and you really can alleviate the need for an EGR valve. I've never seen a difference in fuel economy by removing them on 3 of my trucks, but it keeps the intake manifolds and throttle bodies sooooo much cleaner. Like Joe said, its real reason for using them was to lower cylinder pressure, but supposedly on lighter cars it also had the side effect of helping fuel economy. Make sure you wipe it out in the tune too. I'm inclined to believing that the LS based PCMs were smart enough not to advance the timing with a physically defeated EGR valve, but some earlier OBDI engines were not so smart. My friend lost a 2.2L Toyota Celica engine and we believe the cause was the EGR that was physically disabled with the tune left alone. It doesn't help that the fuel is reduced too. This is necessary with a properly functioning EGR valve as, theoretically, the air injected by the EGR has no fuel or oxygen leftover for combustion so your engine acts like a smaller displacement engine.