Miller (22) won the Super G and giant slalom titles convincingly last week and, in Saturday's slalom, was unchallenged by the other national contenders, finishing fifth overall in an event again dominated by Swedish World Cup competitors.
Frida Hansdotter (22) won in 1min 40.59sec, ahead of team-mates Veronica Smed (19) in 1min 42.79sec and Jessica Lindell-Vikarby (24) in 1min 43.19sec.
Miller, a national team member, recorded 1min 47.16sec as the first New Zealander across the line, giving her the treble and the combined trophy for the national championships.
Miller said she was ecstatic with her victory.
"To get all three titles is a great feeling.
"I am very happy about it - everything has fallen into place for me this week."
The men's race was a tightly-contested event between Winsloe (19), who trains with the Cardrona High Performance Centre, and national team member Tim Cafe (21), of Queenstown.
It was Winsloe who crossed the finish line in ninth overall in 1min 40.79sec while Cafe finished 10th in 1min 41.00sec.
However, it was Cafe who won the national combined trophy, after winning the Super G title and finishing runner-up in both the giant slalom and slalom.
The men's race featured several top-ranked international skiers and the battle for the top three placings was intense.
Urs Imboden (35), of Moldavia, a coach with the Cardrona High Performance Centre, held off a strong challenge to win the race in 1min 35.41sec ahead of Kilian Albrecht (33), of Bulgaria, and Mattias Hargin (19), of Sweden, who finished in 1min 35:70sec and 1min 35.88sec respectively.
Ski Racing New Zealand general manager Simon Mills said the calibre of the races had been "outstanding" and served as a great forerunner to next year's inaugural Winter Games.
Lucy Tait-Jamieson (20), of Auckland, from the Cardrona High Performance Centre, was the second New Zealander in the women's race in eighth, with her sister, Emilie Tait-Jamieson (21), third in 12th.
The third-placed New Zealand man was national team member Angus Howden in 14th.
• The first man to land a switch backside 1260 in snowboard competition has been confirmed as an entrant in the LG FIS World Cup snowboarding event at Cardrona Alpine Resort next weekend.
Mathieu Crepel, of France, accomplished the trick at the world championships in Switzerland last year, where he won the championship title, and is now riding on the Ticket To Ride World Snowboard Tour, led by New Zealander James Hamilton.
A switch backside 1260 is a backwards start into a rotation of 3, combined with a "backside" grab of the board.
Athletes from 19 countries will be in Wanaka for the world cup event, in which competitors earn valuable FIS points towards qualification for the 2010 Winter Olympic Games.
