Yeah, Sawtooths are a bitch. When they attack, they actually attack twice; first the lunge and then a swipe. The key to dodging it is either roll toward the Sawtooth as it lunges so you end up behind it and it can't swipe at you, or roll directly away two or three times consecutively.

Use fire arrows against them, it is their weakness. On easy it shouldn't take many arrows, and when they light up they are stunned for a second which will give you some room to breathe. You can also lay down shock-wire with the tripcaster and bait them into it (either run while he's following you or set it up on their walking path) which will take them out for a decent amount of time or until you crit strike them. Other than that, try to aim for the components on their back, hitting those will deal more damage.

I started a new game on UH, and believe me I know how you feel. I banged my head against that wall during the save Nora braves mission in Devil's Thirst(?). I had to set up shock-wires all around before engaging, and dodge my ass off trying to bait them into it, while firing fire arrows every chance I could.