your A/F ratio is the bottom line. It should be up near the 13 line (yours goes from mid 12's to low 11's) to be optimum. To be honest, its not all that bad really, better than a lot of AU V8 ratio's I've seen.
Theres not too much you can do about it though, maybe try a stock fuel pressure regulator, or get a Chiptorque chip for about $600 that will flatline it in the optimum area. Unichip will do it too... but at $1200 its a bit more expensive.