You will need a couple of long extensions and a breaker bar to remove the the mid pipe to manifold nuts. Make sure you take the nuts off the studs and put them back into the head, some will not go back in after the header is on. Also start all the nuts on the right side before you tighten any up, the tube is in the way to start the bottom nut on #3.
I was able to tighten all but the bottom nut on #3 and #6 with a Box End Wrench from the top, having a ratcheting box end would help. #3 was flipping the wrench around and #6 was from the bottom.
I also unplugged the passenger O2 sensor, it let my exhaust drop a little bit more.
2013 V6 MCA, Performance Package, Security Package, Comfort Package and Electronic Package
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GMR Member 257