Now i know that humans and elfs have to were certain stuff for it to gain. do gargs have something special they have to wear to?
You don't need to wear special stuff, just wear anything until you receive a message like "cannot move unnoticed because you're wear to much blabla" :}
So remove some items until you can move unnoticed and train while you have a reasonably "growing", when it stop to gain or the gain is slowly, wear something heavier =]