What was your A/F? How about the temp and humidity during the test? Did the dyno apply a correction factor for that or is the printout "raw"? Also, I'm guessing that you can probably find a few more ponies with a custom tune. No matter what, your 1/4 times are pretty good, so I wouldn't sweat it too much.
its a mustang dyno, so the numbers will be lower when compared to a dynojet dyno sheet. also, dynos vary between each other, so it is not 100% reliable to compare numbers between dynos. like said previously, the track numbers are a better comparison. the dyno really just measures improvements when modding.