Croustibat

The boost controler is used to keep the wastegate shut longer, and then manage when / how it opens. It results in faster spool, and of course manageable boost. What is even more important is they usually have a warning setting that will open the wastegate and dump a variable %age of boost if you reach a set pressure. This prevents running 18lbs when you set it to 12.

If the AFR gauge says you are good and it is working fine, then you are not running lean.

You DO have an AFR gauge in the car ? What does it read off boost/ spooling / on boost ? What other gauge do you have ?

Did you have your EcU remapped or not ? Or are you just using an SAFC ?
As you are not remapped you could just be hitting the ecu load protection. It cuts fuel at a preset TP value. That value goes up, then down as your VE decrease. It must be peaking around 5/6k and is boost dependent... if you are right next to its limit, a little overboost or lower temp and there it goes, it cuts.



That.

AFR says how much fuel you burn. You want lean at part throttle, stoeich on some parts of the map, and 12 at WOT, basically. Go leaner and you get less power, higher temps. AFRs dont give power, they somewhat prevent you from accessing it. Setting AFRs is very easy, you just need a gauge and sensor

What makes power is timing, and this one is a bitch to set.

Set it wrong and it makes holes in your pistons (too advanced) or gives too little power and too much heat (too retarded, which is sometimes used to spool turbos faster, run retarded just when the turbo starts spooling helps).