5 days gives you ALL of Umbria. The 3-day essentials PLUS Spello (Pinturicchio), Todi (the perfect piazza), Lago Trasimeno (where Hannibal destroyed a Roman army), Montefalco (Sagrantino wine), and a full day in Norcia/Castelluccio truffle country.
Full day. Arco Etrusco, Fontana Maggiore, Galleria Nazionale (Perugino, Piero). Rocca Paolina underground. Lunch at Sandri (Corso Vannucci, pastries since 1860). Evening passeggiata on the Corso. Sleep Perugia.
Morning: Assisi. Basilica di San Francesco (Giotto + Cimabue). Eremo delle Carceri (the hermitage where Francis prayed — 4km above town, profound silence). Afternoon: Spello (15 min). Cappella Baglioni in Santa Maria Maggiore (Pinturicchio frescoes — the most JOYFUL Renaissance painting in Umbria). Roman Porta Venere. Sleep Assisi/Spello.
Morning: Spoleto. Ponte delle Torri + Duomo. Afternoon: Cascata delle Marmore (both viewpoints — lower = spray, upper = 165m drop). Evening: Todi (45 min) — Piazza del Popolo, one of Italy's most perfect medieval piazzas. Sleep Todi/Orvieto.
Morning: Orvieto. Duomo + Signorelli. Underground tour. Pozzo di San Patrizio (double helix staircase, 62m deep). Afternoon: Lago Trasimeno (1h). Castiglione del Lago fortress. Ferry to Isola Maggiore (15 residents, lace-making). Sleep lakeside.
Full day. Norcia: truffle and salumi shopping. Lunch: strangozzi al tartufo. Afternoon: Castelluccio (1,452m) — the Piano Grande. If June: the Fiorita wildflower bloom. Buy lenticchie IGP. Return Rome (2h) or Perugia (1.5h).