The first change here, at bars 12-13 coincides with a phrase, which will help you to keep things smooth. From bar 15-18, however, the shifts also occur mid-phrase, which will really test your ability to shift efficiently.
Here are two pieces to really stretch your position shifts. They both require positions higher than third. First the Maozart Adagio in E minor k.261. The video shows the perfection of Itzhak Perlman's effortless playing.