Welcome to the forums Joe! Sounds like you got yourself a nice deal on that Ecoboost.
That 34MPG you're seeing, is that rating based on what you see in the dash cluster? Just as a FYI I've manually checked every tank of gas that's gone through our 2016 Ecoboost and I've found that the MPG reported by the cars instrument cluster is highly optimistic by about 2 MPG's.
Let us know how the tuning goes with the Diablosport, most guys in here seem to be using the Accessport handheld tuners from Cobb.
2016 Ecoboost Mustang
2009 C6ZO6 - Katech Stage 2 #115
2005 Mustang V6 (Sold)
2003 Terminator (Sold)
2002 Mustang GT (Sold)