Hurting MPG

[Coolguy]

Hey Everyone. I am needing some advice as to what my next step should be. About 4 or so weeks ago I installed a Rough Country 2in leveling kit that came with a 3in rear block and all new shocks and cooper discover AT3's 285/70/17 on stock rims. Since then my MPG has significantly decreased to approximately 10-12 max from stock which was recently getting me about 18 or so when I just recently traveled to possum kingdom lake a week or two before. Any thoughts?

 

My old tire were 265/70/17