Overall, your tree actually looks very healthy. From the photos, I don't see any symptoms that appear to be disease-oriented. And the localized damage, to one small section of the tree, would be more likely to indicate an environmental issue, than a pathogen or insect. I would recommend pruning out the affected limbs and watching for recovery. Be sure to paint the pruning cut to ward against oak wilt. If symptoms return or persist, please give us a call. 512.854.9600. Ask to speak to a Master Gardener.