Fuel mileage drop after questionable fuel.

Now I'm not here to complain about the mileage that I used to get with my stock 05 EAT LGT. I have a question about my mileage after getting a hold of some questionable fuel. I was on the road and had to get some brand of fuel I have never ran before. I only pumped about 5 gal. Before this I was getting the average mileage that I have seen here, but now it has dropped to around 15 city, 18 open road. I tried running two tanks of Mobil fuel system cleaner through, but no improvement. My guess is that I have some crap in the injectors, but I don't know how to fix it.?