Help! My FE has dropped

[zimagold]

I've been averaging 29MPG through the winter on my 98 Corolla - 100% city driving here in Vancouver. As the weather has warmed up, I was expecting my FE to go up even more. But instead, the last two tanks have averaged 26MPG and it looks like the current one will be the same.

I'm doing more coasting than ever. Engine off at lights. Safe drafting whenever possible. I feel my that my hypermiling is better than ever, so a drop heading into the summer is especially troubling.

Before I noticed the drop, my mechanic adjusted the e-brake tension and cleaned the brakes. I don't think the brakes are dragging because the neutral coast seems to be as good as before. Oil has just been changed. Tires always at max 35psi. What am I missing? I think I'll change gas stations to see if they're doing anything funny with the mix.