Shares of United Parcel Service Inc. /zigman2/quotes/201245396/composite UPS 0.00% broke out to record highs Tuesday, as they soared 10.8% in afternoon trading to pace the S&P 500's /zigman2/quotes/210599714/realtime SPX +0.19% gainers, in the wake of the package delivery giant's blow out first-quarter results. In the two weeks leading up to the earnings report, the stock had closed within a relatively narrow range of $175.81 on Monday to a record $179.71 on April 16. What helped boost UPS profit to a record was the American Rescue Plan Act that President Biden signed into law on March 11. UPS Chief Financial Officer Brian Newman said on the post-earnings conference all with analysts said that law prompted UPS to remeasure the International Brotherhood of Teamsters' pension plan at current discount rates, "which have significantly increased since year-end," resulting in a $6.4 billion reduction in pension liability. That helped add a $2.5 billion mark-to-market pension benefit to first-quarter net income, which rose to a record $4.79 billion. UPS stock rally helped push the Dow Jones Transportation Average /zigman2/quotes/210598063/realtime DJT +0.98% up 203 points, or 1.4%, as well as rival FedEx Corp.'s stock /zigman2/quotes/203047719/composite FDX +1.11% up 4.6%, while the Dow Jones Industrial Average /zigman2/quotes/210598065/realtime DJIA +0.04% fell 29 points or 0.1%.