The Dubs were just a horrible matchup for him in general. When he's forced to be mobile on defense and he has to deal with a physical defender like Bogut, who historically gives him fits, he's bound to be exhausted at some point. Compounded with the lack of rest, I'm surprised he was able to contribute in Game 6, even with as little as he could give in the second half.
The Grizz, while being a better defensive team and more physical team-wise, really won't be throwing that sort of game at him. Gasol isn't as physical as Bogut, and Duncan has performed better against him, especially this season. He also has someone he can reliably shut down in this series on the defensive end in Zbo, and by doing so he'll really hurt a Grizz offense already terrible as it is. IMO as the series goes on we'll see a steady improvement in his game as he gets a bit more rest and plays an opponent where he can utilize his strengths.