First thing that comes to mind is... are you ever going to be getting
any custom dyno tuning?  If so you may want to check with your
perfomance shop and see which tuner they use and go that route....

Now please don't flame me when I mention the word "automatic"... but
for cars with automatics the SCT X-Cal2 seem to be the best choice.
The X-Cal2 offer more control over the automatic than the Diablo
Predator... A number of GT folks have switch from the Predator to the
X-Cal2 for this reason...

Now if you are just going to order a tuner then I would have to vote
for an X-Cal2 from Alternative Auto (www.alternativeauto.com)  I live
in Michigan so I've been lucky enough to work with Lidio in person...
great guy, great shop, great performance! Do a quick google on "Lidio
Alternative" and you'll see Lidio has been on the Mustang scene for a
long time!

hth,
john