Well just wanted to give that update on my improved fuel economy after doing the upgrade. While it hasn't been the miracle I hoped for, it has improved and also I have yet to take any long freeway trips which give me my best mileage and would be a true indicator of the improvement. Most of my driving is 60% city 40% highway and 5% of that towing a medium sized trailer. Also my Yukon was running ok before I did the upgrade so if you have injectors that are actually failing this would make a big difference so don't let this discourage you.
Fuel economy since late November 2013 which is when we got the Yukon Anything over 13 usually consisted of more freeway driving than usual. I still don't have enough fill-ups since the upgrade to show much but its better none the less. Also need to consider than its been hot as hell out here in CA and I've been having to run the AC pretty much since I did the work I doubt it has too much change on mpg but just take that into consideration.
Pre upgrade mpg
11/19 11.761mpg
11/27 12.344mpg
12/6 12.694mpg
12/13 12.025mpg
12/23 12.118
12/28 13.499
1/11 11.557
1/24 11.73
2/4 12.448
2/14 13.58
2/21 13.821
2/22 16.404 - All freeway
3/8 13.086
3/14 14.37
3/18 15.37 - All freeway
Post Upgrade
4/1 12.948
4/12 12.685
4/18 12.78
4/30 13.865
Haven't done the math but it looks like at least a .5 mpg increase.