By Scott Leith, The Atlanta Journal-Constitution Knight Ridder/Tribune Business News
May 13--In the soft drink business, what goes up often comes down.
Vanilla Coke and Mountain Dew Code Red, the industry's biggest new products of recent times, have seen their sales slide after first taking off with U.S. consumers.
Some of the declines are to be expected -- new brands tend to enjoy a spike in trial sales before settling in with a routine group of buyers.
But the falloff in sales is still striking and a sign of how tough it is to get consumers to keep on buying.
In the first quarter of 2003, Mountain Dew Code Red's sales volume …