I've been thinking about this for a bit, and I guess the only thing I can post is speculations... So, please don't get offended thinking that I'm assuming anything about you or anyone else. I'm just speculating!

My average for the first two years that I owned my car was about 43 or 44. I remember being super frustrated the first little while when the best I could get was 42.7 per tank. I hadn't found GH to get tips from yet! Eventually I just sat back and enjoyed the ride, got to know my car, got to know what made it more effiecient and what didn't.

Lately (after 2+ years driving it) I've been getting 46 mpg, and this tank 48.8 Started going up when I made sure my tires were pumped properly and a bit higher than usual. I also don't drive over 72 mph-- that seems to be the point when the FE drops faster. I've been practicing the tips.

Anyway, my first speculation is that maybe you're like me. It takes time to "break in" the car, or maybe it's to "break in" you as a driver. Even after reading all the tips on this forum it take practice to do them right.

The other thing is, I definately notice that I get higher MPG on the first part of my tank, and that sometimes it falls as it goes. For the first 50 miles or so it does the usual fluctation of low and high as the averages play out. I think it still does that as we go, but is less noticable. I don't have any guess as to why, except that it's harder to budge the real average the more miles you go... and the more miles you go the more it's closer to true...

This doesn't explain anything about getting 42 mpg after resetting for the last 300 miles of a tank. Sometimes, despite everything, the average on a tank sucks.

Here's another speculation. Maybe you need to switch gas stations. Or consistantly go to just one. I have recently been going to one more than I used to, and going less to another. Sometimes I notice that if I fill up elsewhere the average changes. "They" say that all the gas comes from the same place. Maybe so, but petrol from some stations ends up with worse FE than others!

Ok, anyway, enough of my rambling. Major points: You're not alone. Relax, enjoy the car--you're doing better than most cars on the road anyway!
--A