There might be something wrong with the normal blending in your triplanar shader. If so, you can easily fix that: http://blog.selfshadow.com/publications/blending-in-detail/ . The UDN approach works pretty good and is fast, too.

If all your hills are looking like this, then i wouldn't bother with triplanar texturing though. For a terrain it only makes sense for steep angles, like cliffs and the like ... or if you are using voxel terrains