Car is an 83 245glt with intercooler kit. Lately it has lost a lot of power when running full boost even though the boost gauge reads just into the red at 3700 rpm. The engine roars, it sounds like it wants to go, but the acceleration just isn't there anymore. It's actually still not bad off the line, but the torquey feeling it used to have at high rpms is pretty much gone.

In the last week I have checked every system I can think of that could cause this. There are no big vacuum/boost leaks anywhere, both fuel pumps and fuel filter are new, fuel pressure is good, lambda system/frequency valve are functioning correctly, ecu checks out good, timing is correct, timing retard on the distributor is working properly, boost enrichment switch is working properly, turbo spools up quickly and isn't making any weird sounds, cat is gutted so exhaust restriction is unlikely, timing belt is new, all ignition parts only a couple of months old, air filter is good, and I am running 94 octane Chevron in the car (fuel and oil consumption aren't too bad either).

Anyone have any ideas about obscure turbo problems I could look into? I'm sure there must be something very obvious that I'm missing.
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'83 245glti