Gallop Poll - Mondale 48%, Reagan 46%
Gallup nailed 1984 right on the nose at 59-41 Reagan.
Here are three sources. There are many more. You received some bad information somewhere. In fact, Reagan lead Mondale all the way in 1984 as charted in the Gallup Poll table seen in the 3rd link, including by 10+ all the way from July through election day.