Also Vinny Testaverde and Alex Smith. Both were former #1 overall drafted QBs who were terrible in their first 3 years or longer. They eventually had long careers as productive serviceable-quality starters with the right coaching staffs.
Testaverde became a Pro Bowl QB in his 10th and 12th seasons. His TD-int ratio began improving in his 7th season. Alex Smith began leading his teams to the playoffs in his 7th season and beyond under Harbaugh and Andy Reid. His 5th season was his first productive year in passer rating and TD/ints.