1987 744Ti 177K

Car is new to me, picked it up as a parts car at the Goodwill Auction. It had a blown hose to the intercooler. After replacing that it ran much better (grin).
It still does not run right. The boost gauge indicates that it is boosting normally but it is a real dog. It has poor acceleration but once at speed seems to be able to maintain it well enough. Starts fine, idles fine, shifts fine; just your basic dog in performance. I haven't had much time to look into it but want to do that now. I plan to run a compression test and check the cat. I am inclined to think the cat may not be the problem because it seems to hold the boost gauge while trying to accelerate. I feel that if the cat was clogged it would be impossible to hold boost at normal level. Anyone have experience with a restricted cat on a turbo car. What was the behavior?

Other than checking the cat and running a compression test any suggestions on what to look into to turn this car into a decent performing brick? Thanks.

Randy