Fault code 17964 is driving me crazy.

only happens when:

In 6th gear just over 2k at 70mph going up a incline.

Changed map sensor n75 valve and all vac hoses.

I don't think it's sticky vanes as it goes well in all other gears.

I'm still running the standard boost hose out the turbo and then into the forge piping. Noticed a bit of oily residue on this joint but I doubt if this is leaking it would cause limp mode.

Anyone else had trouble like this. If I stick to 60 it's all fine. Drop to 5th and it will go like a train to overtake up a hill.

Any advice is helpful

I had a boost leak on that pipe from the turbo. Caused no issues except the noise. Replaced the pipe but drove for a day with the leak & had no fault codes when I checked afterwards. Can't help anymore than that though I'm afraid :-/

negative boost is usually something else other than sticky vanes. "Positive deviation" is the overboost code. You are getting underboost so it is leaking out of somewhere. Would recommend someone using a smoke machine, pushed in at the inlet manifold end, and see if anything leaks out anywhere.

Must have a leak as just over 2k rpm must be max ish boost. I'll stick her on ramp and have a inspection.

Do awesome do smoke testing?