How to get rid of terrain splatmap texture seams?

I'm trying to manually texture a terrain with a grid of images using a splatmap. The images are exactly 256 x 256 and I seem to have everything working fine except for the edges. I've checked images in PS and they line up nicely, but in engine there are obvious seams (image below). I've turned off mipmaps on the textures, and have tried to set the textures wrap mode to clamp, but none of that has fixed my issue. Any ideas? Or is there another way I can tile a terrain with images? ![CLEAR SEAMS][1] Thanks for any help!! [1]: /storage/temp/44069-borders.jpg