theres a thunderjaw site where you can kill(need tear arrows) thunderjaws, go to campsite, quick save then reload and keep doing it for xp/mods/shard and sell the mods for more currency. i used it more for the mods to sell and use than lvls. lvls only give you like 100HP extra and thats it. no extra dmg or anything like that so its not really necessary for you to lvl up. i beat the story at lvl 29.