no point in tuning to counter natural power loss. Fix it first, then concentrate on power mods later.
What i normally do when i buy a new car and/or service for the first time is run a bottle of engine flush through the oil for about 15 minutes, replace the oil and filter with origional alfa specced items (selenia 20k etc). Replace the sparkplugs, replace the airfilter and then clean the throttle body (easy enough to do, just take your time and make sure you remove it from the car to clean it).
After that i give the engine a tank of fuel to recover before adding some injector cleaner.
I always use FORTE branded products for engine cleaning (Forte advanced motor flush for oil flush and Forte specialist injector cleaner for the injectors).
If you don't notice a power improvement before the end of the tank then i would look next at the sensors. Either the MAF or Lambda could be playing tricks.