Sounds like you have some problems un-related to the turbo if it stutters under vacuume. One thing it could be is the TPS sensor, there was a turbo supra that was having some hesitation under partial load because the tps was out of wack. It might be sending out a lower/higher voltage to the ECU and screwing up the air/fuel ratio. I actaully think mine might ave the saem problem. anotehr problem might be that I had my TB bored out and used the sensors that was on it (off a 95) so maybe the tps is old and screwed up.
I guess the TPS sensor is pretty sensative, any water or condensation in it and they get screwed up. Another thing it could be is an over active knock sensor, the only way to know this is to check what your timing looks like under load. hopefully it should be in the high teens?
As soon as I get home and get my Data collector I'm all over it!
I should have never got my TB from Mutiny Racewerkz... DAMN!!!

Wyatt Leras
http://www.turbogs.dsmpower.com
98 Eclipse GS Star Stage 5,000 Turbo kit