"Peak Performance." Kartes. $19.95. Genial Charles Garfield lectures an audience of smiling yuppie execs anxious to Improve Their Performances. This hourlong exercise is harmless enough, possibly even useful to a few determined achievers who'd be achieving anyway--but what a snore. With fervent sincerity, Garfield lists Five Basic Skills shared by all Peak Performers (learned skills, not genetic endowments, he insists), using corny, shamelessly sentimental anecdotes to illustrate his points. Sample skill: Motivation Through Mission. We get to hear again about Lee Iacocca's drive to succeed.