WASHINGTON (AP) — The nation’s top economic forecasters have become much more optimistic about the U.S. economy, predicting that increased vaccinations, stronger job gains and more government support will lift economic growth this year to the fastest pace in nearly four decades. The National Association for Business Economics said its panel of 49 top forecasters expects the gross domestic product, the country’s total output of goods and services, will expand 6.5% this year, the biggest annual gain since a 7.2% rise in 1984. The new forecast is an upward revision from March when the group was expecting a GDP gain of 4.8% this year.