They make wheat tortillas & "low carb" ones. Both are pretty good & taste fine. I don't know were either of them are on the GI index though.
I've noticed that the low carb ones have an obsene ammount of fiber (something like 11 grams per tortilla).
1) that fiber likely puts them low on the GI Index
2) I'm not a huge fan of the flavor, but, when dieting, could be a lot worse
3) I think the fiber comes from added soy flour, wheat gluten, etc.