Allegorithmic Substance Painter would be great for what you want as you can see what the object looks like as you change the texture, you don't even have to buy the software fully, you can just rent it for a month and do a few models at once or buy it over time (this is what I am doing, I wouldn't use anything else). The only thing is you would have to change the object from the type in GG to *.fbx,*.obj, *.dae or *.ply as this is what SP uses, but that is fine since there is a great site that can change the type of just about anything.
Online 3D Converter:
http://www.greentoken.de/onlineconv/
This is a great site I have used it many times and never had a problem with the models it produces.
After you are happy with the new texture of your model you then just export the Texture files out and convert them to *.dds, this is easy enough and there are many free programs that will do it too like
Easy2Convert JPG to DDS (Another program I use all the time with great results)
Hope this helps
Andrew...
HP Pavilion Laptop - AMD A8-4555M APU with Radeon(tm) HD Graphics - 1.6GHz, 8GB Memory, Windows 10 Home, 64-bit Operating System.
I've got something to say - It's better to burn out than fade away.