In the World Cup , Gruber achieved their first podium places in the 1996/1997 season with a second and a third place in Toblach . In the overall World Cup, he achieved sixth place with the same number of points as the Austrian Gerhard Pilz . In the 1997/1998 season , Gruber won the overall World Cup for the first time with three wins in Kronplatz , Oberperfuss and Železniki and a second place in Mölten . He was able to repeat this success in the 1998/1999 season with two wins in Tiers and Aurach as well as two second and one third place. Gruber won the overall standings in front of his compatriot Anton Blasbichler , who also scored two wins, two second and one third place, thanks to his better result (fifth place in the first race of the season compared to seventh place by Blasbichler).
In the 1999/2000 season Gruber only contested two World Cup races, which is why he fell back to 21st place overall. On January 14, 2001, he celebrated his sixth and last World Cup victory in Lüsen , after having achieved third place at the World Cup in Unterammergau at the same time as the Austrian Ferdinand Hirzegger a week earlier . In the overall World Cup he reached sixth place in the 2000/2001 season with two more top 10 results. In the 2001/2002 season he contested his last two World Cup races, but was no longer in the top ten.