I have indeed cleaned the entire upper and lower.
I sent it back to SIG and the note upon return says:
"We replaced the gas return o rings and ran 2 clips (60 rnds) through it and had no malfunctions. " - Sig
I have read that the enhanced has a shorter travel in the bolt and cycles faster sometimes causing feeding problems. You can see this on Youtube http://youtu.be/mSbLragkC54
"The rate at which the bolt carrier assembly recoils rearward can have an effect on reliable extraction and ejection, even if extractor and ejector dimensions and springs are absolutely correct. The period of time during which the bolt is behind the stack of rounds in the magazine, neither traveling rearward or forward, has an effect on reliability in that the magazine may not have enough time to push the next round into place before the bolt comes forward again, resulting in a "bolt over base" malfunction that is most commonly seen on suppressed rifles, as they have much greater rates of fire. Also, high forward bolt carrier velocity can result in extreme bolt bounce, as noted previously, while low forward bolt carrier velocity could mean that there isn't enough force to overcome strong magazine springs, dirt or debris in the action, etc."
This is causing the feeding issues as well as the possibility that the o rings fail in the gas piston.
I am not impressed. I think the enhanced version is a loser and the solution is replacing the upper with another Make, at a SIGnificant cost to me.
We shall see what happens when I pick that gun up at my friends shop and shoot another 120 rounds through it. If it jams even once I'm going to be ripSh1t.