By John S. McClenahen The U.S. Commerce Department is slated to release first-quarter 2004 GDP data on April 29, and a strong economic showing is anticipated. The big question is just how fast the U.S. economy grew during the January through March quarter. UBS Investment Research, New York, is looking for a 5% inflation-adjusted rate, which, it notes, "would put the year-over-year growth rate at 5.1%, the highest since 1984." Merrill Lynch & Co., also based in New York, now forecasts a 5.3% rate for the first quarter, "led by the continuously consuming consumer." In contrast, as recently as April 2, Merrill was projecting only a 3% rate for the first quarter of this year.