i put a "detroit locker" in my 2000 jeep cherokee about 5 years ago and it was a U.S. made part then.
as to the labeling "Made in the U.S." - i believe it is Federal Law that all parts carry a label indicating the "country of origin." SOME auto parts now say on the box "assembled in the U.S." or "assembled in the U.S. from parts world-wide." as to the "legality" of the labeling "Made in the U.S." - you would have the legal right to return the item to the vendor asking for a full refund under the "truth in labeling" federal commerce laws. if you do decide to "lawyer up" and get your money back, you are entitled to ALL your money back - a miss-labeled part is considered to be a "deceptive" part. thus, you cannot be charged a "restocking fee." further, if you filed a suit at your local magistrate (or District Justice) alleging "deceptive trade practices" (which is the legal term for this kind of suit), you could also ask for all your damages including the cost of shipping the part back to the vendor.
i would urge you to send this part back to the vendor. MAKE SURE that you take pictures of the box showing the "Made in the U.S." label and also a picture of the "Made in Taiwan" stamp on the part itself.
good luck...