Boost fade

[asshanson]

I have a 96 Tsi with a 3" exhaust and an FP T-28 turbo. I run about 18 lbs of boost, but it doesn't hold - it fades to 14 by redline.

I've checked for boost leaks, 99% sure there isn't one. I've changed boost controllers, same thing happens. I actually tried a broken boost controller too and it didn't limit the bost, so it went to 25 almost instantly at 3500 rpm and I let off.

What else can cause this? I assume the T-28 can hold over 18 until redline, so I doubt that's the issue.

Any ideas???