Lean codes mean there's more O2 in the exhaust gases than the MAF metered. This can be caused by a dirty MAF, vacuum leaks, exhaust leaks, PCV leak, too low fuel pressure, and so on....
So, you should first clean the MAF with special MAF cleaner and don't use "sport" air filters.
Could you also please post the exact temporary and permant codes you have seen since you have that problem? Solving a puzzle without all parts is impossible.
Lean code after hard driving sounds like an exhaust leak, so check the connection between cylinder head and turbo manifold. Burnt gaskets and loose/missing bolts on the manifold are really common on T6s that get frequently floored.
Also check the PCV/oil trap and the small hose from the PCV towards the intake pipe. If your car "whistles" after cold start, replace the PCV.
Also check the duty cycle of the fuel pump and fuel pressure while driving.
What fuel are you using? Anything below 98 octane is a no-go if you floor it on a regular basis.
