I was about to chime in with a "try another MAF" before reading your last post. The 09 is a PWM unit, which means it reads in HZ not 0-5V like an LBZ or older units. So a flaky harness wire would most likely result in zero signal or the correct reading. Not a low reading.. Glad to hear you fixed it.
Funny story last week totally related, from my new daily 6.7L powerstroke. Starts setting a MIL for MAF. I check it with a SnapOn and it reads 432grams per sec at key on, and 433grams at WOT. Ok, bad MAF.. Replace the MAF, no change code remains.
Get on the PS forums and run the code"s", because I completely overlooked the GPCM and Network error codes when I saw the word "MAF". Very common issue. Was just a blown fuse due to a open sensor connector back on the frame rail I'd forgot to tape up. Found it funny the MAF actually tracked correctly, but way off scale...