2011 A3 TDI 2.0 in Canada. Deleted DPF and EGR, .5 tunezilla tune. Consistently get P00AF (boost controller) and P0299 (underboost condition) with limp mode. For the delete we just opened, cored the DPF, welded shut and reinstalled, plus EGR blocking plate at the EGR. Codes appeared immediately. Replaced the N75 and the turbo actuator plus ran adaptation. Turbo vanes are smooth as glass and operate freely with no restriction when actuated by hand. Voltage for actuator is in spec at full and zero vacuum. Vacuum pump is in spec. No vacuum leak that we can find. N75 voltage is correct. Replaced the Boost Pressure Sensor too. Even flashed back to stock and reloaded delete and tune.

Car wants to see more boost than is producing. Limp mode seems to come when asking for "just a little more" power like a long sustained hill at the 100kmh and 2000rpm zone. Car drives fine when city driving and under load like hard accel. 

We are officially stumped. including my local VW guy who tunes and races. Next steps are to remove Cat and drive to see if it's clogged. or go ahead and replace all the vacuum lines. I'm also considering trying to load the delete with no performance tune. I'm not convinced it's the turbo failing as the car had zero issues with boost prior to delete, all issues were downstream, hence the delete. 

Any ideas from the hive mind?

I have since tuned back to "stock" with deletes in hopes the extra power was the issue. That didn't do anything. Also put in a new O2 sensor, nothing. 

I'm now beginning to think it's either the turbo needs a clean, or something to do with electrical.