Final answer:
IRS Revenue Rulings have the highest weight of authority among the given IRS pronouncements.
Step-by-step explanation:
The highest weight of authority among the given IRS pronouncements is IRS Revenue Rulings. Revenue Rulings are official interpretations of the tax laws and are issued by the IRS to provide guidance on specific issues. They have the highest weight because they are based on an extensive analysis of the law and have been thoroughly reviewed and approved by the IRS.