As part of its midterm evaluation of the 2022-2025 light-duty greenhouse gas (GHG) standards, the Environmental Protection Agency (EPA) has been acquiring fuel efficiency data from testing of recent engines and vehicles. The benchmarking data are used as inputs to EPA’s Advanced Light Duty Powertrain and Hybrid Analysis (ALPHA) vehicle simulation model created to estimate GHG emissions from light-duty vehicles.For complete powertrain modeling, ALPHA needs both detailed engine fuel consumption maps and transmission efficiency maps. EPA’s National Vehicle and Fuels Emissions Laboratory has previously relied on contractors to provide full characterization of transmission efficiency maps. To add to its benchmarking resources, EPA developed a streamlined more cost-effective in-house method of transmission testing, capable of gathering a dataset sufficient to broadly characterize transmissions within ALPHA. This technique targets the range of transmission operation observed during vehicle testing over the EPA city and highway drive cycles.This paper describes the method and test results of the benchmarking process used to gather transmission data. With this method, the transmission is tested as a complete system, as opposed to disassembling the transmission components and testing each separately. To develop this test method, a 6-cylinder EcoTec 4.3L engine with a 6L80 six speed automatic transmission from a 2014 Chevrolet Silverado was installed in an engine dyno test cell. The transmission dataset includes gear efficiencies, torque converter slippage and K factors, oil temperature and pressure, and OBD/epid CAN bus data.The transmission data collected using this benchmarking method were supplied as inputs to the EPA ALPHA model including transmission gear efficiency, torque converter K factors, and spin losses. The ALPHA results were then validated to vehicle chassis dynamometer test data.