Couple more thoughts -
*Higher gravity mashes usually result in lower efficiency.
*Mash not mixed well - dough balls.
*Channeling of sparge water through grain bed.
In my experience, 1.07's is where I start losing some efficiency compared to what I am used to on lower gravity beers. I routinely get 80% efficiency in the 1.04-1.06 range. As soon as I go for 1.07's though, I tend to start falling short of that same efficiency.
I would test the hydrometer though, just in case.
Kegged/Serving: British Dark Mild, Oatmeal Amber, Pliny Clone, Porter, Bo-Pils, Oktoberfest, Stong Scotch Ale
Bottled: Barley Wine, Bourbon Barrel Porter
Primary: American Pale Ale, American Brown Ale, British Bitter
Secondary: Sour Cherry Stout, Sour Belgian Golden on Cherries, Bo-Pils, Belgian Strong Dark
Future Brews: British Dark Mild, German Alt, Porter, APA, American Brown Ale