SAVANNAH — The Georgia Ports Authority achieved its highest month on record in March, moving 2.61 million tons of cargo — a 15.5 percent increase over the same month a year ago. The 349,682-ton increase was powered largely by double-digit container growth. The Port of Savannah’s Garden City Terminal moved 260,539 20-foot equivalent container units (TEUs) during the month, up by 28,000 TEUs or 12 percent.