ALH P1556 Diagnostic Code + limp mode help

[Chuck1978]

'02 Jetta ALH. P1556 diagnostic code, + limp mode.
I found conflicting descriptions for P1556, one said that more boost was detected than expected, the other said less boost detected than what was expected. I would go with the less boost option, but I am uncertain. One was from a Haynes manual.
I've replaced several sections of vacuum tubing, and unhooked MAF sensor per online advice "unhook MAF, if performance improves, then replace MAF,  as computer will substitute a safe default value in it's absence."
Well the performance did improve slightly unhooked, I can get 5 or 7 PSI boost with the MAF unhooked, no boost with it hooked up. Before and after replacement, no change. Bosch replacement part.
Car has EGR delete, so I swapped the N75 boost control solenoid for the abandoned EGR control solenoid. Still no change! EGR solenoid was of unknown history/condition, however.
Is there a MAP sensor that should be my next likely suspect?
I can hook my MityVac up to see that yes, the vacuum pump is definitely working, and I can also hook my MityVac up to the turbo and start pumping a vacuum on the boost controller, and it immediately starts whining and purring, building boost.

Advice?

[Chuck1978]

I also developed a major oil leak on the feed line to the turbo, exact same place I have had three major leaks on my old 1983 1.6TD-IDI (in '82 Rabbit pickup). I doubt this is related, as the oil leak started a while after, and I don't think the P1556 code indicates anything about oil pressure problems

[Dennis Froelich]

Is the actuator working? It could be sticking or have poor vacuum to move it as needed.
Just a thought.

[Chuck1978]

Yes, I put my mity vac pump on the actuator, and started pumping, and it instantly started building a lot of boost.
I do not have vcds / vag-com etc to manually cycle the n75 valve via the computer. Testing the vacuum available on the turbo side of the n75 would be ideal. I have plenty of vacuum on the other side of it as far as I can remember.

It is sitting outside and I have just parked it for the last couple of months, so it hasn't been too much of a priority to work on it outdoors in the winter. We drive a '97 Subaru Outback 2.2L SOHC beater  in the salty snow conditions in the winter anyhow...