It does make less horsepower, and you're in the right area, but I can't remember the exact numbers. The reason it makes less horsepower is because the boost on the automatic TCs is turned down to a 10psi limit so they don't tear the tranny up. Also, the '87-'88s had a smaller (IHI) turbo compared to the '83-'86 (Garrett T-3).
Rick