A major problem people find with grapes is either too much shade or insufficient or unbalanced minerals in the soil. Time of planting is also critical...should be coldest months of fall or spring in my climate. I've been to Southern Greece several years ago with my dad and brother but I surely didn't pay much attention to the what was growing well there except.....well, you should be able to guess.
my vines have problem with too much sun. maybe the roots need more time to establish. it might be soil as well.