Yeah i'm finding exactly the same, fortunately GameGuru has adequate built in ambient occlusion, so not having an AO map isn't a huge issue, hiding seams is difficult, i'm getting around it on my model with a fair bit of mirroring UV's and hiding seams i can't mirror behind other geometry, it's working ok so far.
My biggest issue at the moment with GG though is normals and smooth shading, they look warped in GameGuru when smooth shaded, i don't know if it's a common issue or just blender not exporting smoothing groups, a decent texture can obscure it to an extent, but i've found so far the only way to be sure to get it working right is to either split sharp edges or add supporting edge loops next to sharp edges, any tips you can give me?
i7 7700,k NV1070 8GB, 16GB 3200mhz memory, 1x 2TB Hybrid, Win10.
i5 4760k, NV960 2GB, 16GB 2333mhz memory, 1x 2TB Hybrid, Win10.
i5, NV1050 4GB, 8GB memory, 1x 1TB HDD, Win10.
i3, Intel 4000 series graphics, 6GB memory, 1x 500gb HDD, Win8.1.