What Breed(s) is My Lab Mixed With?

He's just over 2 years old. The Lab is predominant, for sure. However, he has light brown patches behind his ears and on his neck (the ones on his neck are only visible in sunlight). He's a bit smaller than a Lab should be.

About 15-20 lbs lighter. His tail is longer than Labs and bushy. His temperament is also different than Labs, he is much more "testy" and irritable. Any help would be awesome. Thanks!

By Liz