United States international Altidore, 23, scored only once in 28 games for Hull but proved to be deadly in front of goal during two seasons in Holland, notching 31 times last season for AZ Alkmaar.
Altidore told the Sunderland Echo: "I think I just became a better player in Holland than the one when I was at Hull.
"On and off the ball and linking up with the players around me, I just got better. It's that simple.
"I've become a much more confident player since then.
"The two leagues are completely different, but we're trying to play football which looks good and hopefully I can score some goals."
Altidore has also scored in four consecutive internationals for the United States in June.