Good Morning America beat rival Today last week in total viewers and the adults 25-54 demo by the widest margin in 18 years. GMA outperformed its NBC morning-show rival by 883,000 total viewers for the week of August 27-31, the largest victory for the ABC show since the week of May 16, 1994. Among the key demo, GMA has 1.969 million compared to Today’s 1.817 million, the widest gap since the week of August 15, 1994. It was a week of upheaval on GMA last week: As expected, anchor Robin Roberts announced that August 31 would be her last day on the air before leaving to undergo a bone marrow transplant. Still, except for a bump during the London Olympics, Today has lagged GMA for eight of the past 10 weeks this summer.