Since taking the beast out of her winter cocoon, with all the ususal springtime freshen-ups, oil change, etc...I'm noticing a significant drop in mileage. I'm used to getting right around 40 mpg, now it's more like 33-34 mpg. There's just shy of 15K miles on it now. Not sure what could account for such a big drop. Tire pressures are where they're supposed to be. Any ideas? Thanks.