Letter carrier John Groves sorts mail for his route. He and his colleagues delivered a rec-ord amount of mail to Utahns' homes and businesses last year. A 4 percent increase in mail in 1988 meant that an average of 14 more pieces of mail were delivered to each postal stop over the course of the year. Each day the Salt Lake Management Sectional Center, which covers all of Utah and the northwest portion of Nevada, delivers 2.7 million pieces of mail _ "that's 478 pieces of mail for every man, woman and child in the area" over a year, said Postmaster Kenneth R. Prentiss, for a total of 828.8 million pieces of mail in 1988. The Salt Lake management center employs 4,050 people and hired 203 employees last year to handle the increasing workload. Carriers drove more than 7.3 million miles to deliver mail to 497,000 addresses _ 8,000 of them new.