I'd say that the key to playing repetitive lines is to keep at it (practice at slower speeds and build up your speed and stamina) and also try to relax so that you can play with a lighter touch, both with your fretting hand as well as your plucking hand.
I'm having to learn 'Don't Stop Moving' for an upcoming show and had the same issues when I started playing it, but it's all good now.
Cheers, Pete.