I totally believe the 47hp.
MM&FF got either 17 or 22hp on a bonestock 96-98 GT with the SLP exhaust. And SLP claims 30hp on a bone stock 2k3 GT. Yes I know it includes the LT headers, but still...
If it is 25hp with the CAI and 22hp with the X and Catback and TB, I bet there's probably another 15hp in the headers. It's like an exponential efficiency. Seperately, small change, but together Ka-ching.