Where did you download GregTech from? If it was from the GregTech thread on the IC2 forums make sure you either get it from the second post under the spoiler 'Downloadlinks of older and stable Versions', '1.5' spoiler. Or you download Unhinged and get it from there. Both are the same version 3.11
You might also have to tweak the configs a little as GregTech and Tinker's Construct do not play well together without doing so. I'm not sure of the config settings myself as I just play with GregTech only.