Yes, St Francis did struggle with a temper problem for many years but overcame it. The source of this biographical information is presented in Introduction to Devout Life by St. Francis de Sales (Author), Allan Ross (Editor, Translator):
St Francis by the very constitution of his body was of a lively
character and inclined to anger. But having proposed to himself to
imitate that Jesus who had said: "Learn of Me, because I am meek and
humble of heart" (St. Matt. xi 29), he was able, thanks to the
continuous vigilance that he exercised and the violence to which he
subjected himself, to repress and curb the motions of the soul to such
an extent as to become a living copy of the God of peace and
Fr. Alban Buter's biography of him says:
He was indeed naturally of a hasty and passionate temper, as he himself confesses; and we find in his writings a certain fire and impetuosity which renders it unquestionable. On this account from his youth he made meekness his favourite virtue, and by studying in the school of a God who was meek and humble of heart, he learned that important lesson to such perfection, as to convert his predominant passion into his characteristical virtue. The Calvinists ascribe principally to his meekness the wonderful conversions he made amongst them. They were certainly the most obstinate of people at that time, near Geneva: yet St. Francis converted no less than seventy-two thousand of them.
From St. Jane of Chantal's deposition of him for his beatification and canonization, "32nd Point: Gentleness" (ref:1571.7 of The Saint Francis de Sales Collection):
I have never heard that our Blessed Founder was seen to lose his temper. Once I entreated him to be a little roused by some opposition which was troubling our Convent of the Visitation. He answered: “Would you have me lose in a quarter of an hour the small stock of gentleness which I have been painfully amassing for the last twenty years?” It was, therefore, a common saying that he had actually no gall, and indeed, after his death the surgeons found none, but in its place numbers of little triangular-shaped stones, showing plainly the constraint and force which he had put upon himself to conquer the passion of anger. Indeed he told me once, on an occasion of most justifiable wrath and indignation, that he was obliged to rein in his anger with both hands in order to stop it.
That he had been "painfully amassing" a "small stock of gentleness", "for the last twenty years" (since at least the foundation of the Visitation order in his later adulthood, 1610) shows that since until his 30's or so he had not been "amassing" gentleness.