Picked up the truck today. Cost of repair: covered under warranty, no dollar amounts on the paper work but I was told GMC paid the dealer for 28 hours of work. They remove both the bed & the cab. Washed out the tank, replaced everythring from the tank to, and including the injectors. The repair manager says the pump is updated, not the original 2011, supposedly the injectors are also updated. This is the 10th fuel replacement they have done on a 2011, supposedly no 2012 failures. This by the way is a small dealership serving a large rural area in Western US so they do see a lot of trucks.
On a 120 mile return trip the indicated MPG increased from its previous 16-17, no load highway to 22mpg, hope this lasts. Will be back to hauling a load next week
The dealer ship of course has no insight into why.......so no advice on keeping it from happening again. They claim none of the other 10 have had further fuel issues. If this was a fuel pump quality control issue then for 2011s its a roll of the dice and additives or a filter would not have prevented the issue.