It will run lean without a map the Ecu can only compensate so much and your asking it to correct after the event lamda says oh you're running lean let me add fuel, you've already run lean to start with,, not to mention at WOT the standard lamda doesn't work properly once on boost.
Have to disagree with robs first post about letting it be and just do it, this worked as stated on the standard map on the classics in part because the standard map was quite rich as a precaution by design. It is however far from ideal.
Spend the money and get a good map done for it. I would also advise not to chase dyno results
