A lot would depend on the size & format of the original textures. If this is a 16-bit Extended BMP format like DXT3 try saving it without Mips. There's an option for this in DXTBmp & some say it makes all the difference. This might depend on your video card & display settings. You could also try a different format like Extended 32-bit. Each time you edit a texture saved in a compressed format you will lose definition so it's best to work from a master copy & update from that if necessary.