I've searched this thread and the TC thread but have found nothing about what I've discovered, though I may have missed something.
While using GregTech 3.08g and Tinkers Construct 18.104.22.168, I cannot create certain items from TC. I also updated GregTech to 3.09g and Tinkers Construct to 1.4.dev.18 and the issue still exists.
While trying to create stone items from TC to create tool item casts, these seven stencils will produce a GregTech item instead of the desired TC item:
Tough Tool Rod (14279:14) --> Ender Eye Dust (31992:1)
Large Plate Pattern (14279:16) --> Data Control Circuit (31990:1)
Broad Shovel Head Pattern (14279:19) --> Shows unknown item texture, no text (31989:1)
Large Blade Pattern (14279:20) --> Deuterium Cell (31991:1)
Hammer Head Pattern (14279:21) --> 60k NaK Coolant Cell (31988)
Full Guard Pattern (14279:22) --> 180 NaK Coolant Cell (31987)
Arrowhead Pattern (14279:25) --> Portable Scanner (31985)
Obviously, removing GregTech lets the Tinkers Construct items be created with no problems. Also, if an item is created this way, the material cost for the stencil is used up. Example, creating Ender Eye Dust with the Tough Tool Rod Pattern (Material Cost: 3) will remove 3 cobblestone for the cost of the Ender Eye Dust. All of the GT items created this way have the correct material cost from TC taken away. Thus, you can exploit this by creating 180k NaK Coolant Cells for the low cost of only 3 cobblestone.
This should not happen. Check ID's in your configs, and grep your ForgeModLoader log for the word "CONFLICT"
EDIT: Also enabling NEI's ID map dump feature is the most useful feature you'll ever enable. When you track down which ID's are conflicting, just move one of them to an unused area as indicated by the ID map. There's still potential to run into problems though, so don't trust it as the only thing right in this world, because in reality nothing is right in this world.