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: Session IPA, Dark Mild, Ordinary Bitter, Blonde Ale
Bottled: Barley Wine, Sour Belgian Golden on Cherries, Sour Cherry Stout
Primary: Dark Mild, Helles
Secondary/Lagering: Alt, Scottish 70, Dortmunder, Bo-Pils
Future Brews: Heady Topper Clone, Session IPA, Hop Fu, Porter, Plain ol American Ale More...... More....... Beer.......