Sport mode in Saab kills/helps fuel economy?

[AbeisAverage]

I drive a saab 900 se 1996. It comes with a sport and a winter driving mode. My friend was explaining to me that the sport mode keeps the car in lower gear longer to get the most out of the gear before it shifts. He made it sound like that would be bad for fuel economy, and it made sense to me that it would be.

So I've been driving my saab out of sport mode for about a month watching the fuel economy not so much for my pizza delivery job because of the amount of variation. But my other job involves driving to a specific point each day then back home. I've been watching my fuel economy and I've been noticing a pattern of about 23-24 mpg there and 25-26 on the way back. I changed to sport mode and I've been easily attaining an extra mpg both ways. The weather's been same for a while (really hot). I didn't really change any other habits.

So is my scangauge being cheated somehow? I've noticed regardless of being in sport mode or not, sometimes when I let off the gas or switch to neutral on my glides the instantaneous mpg will jump to 9999 like when the scangauge turns on. I don't think it's my scangauge because when I plugged my friend's in it did the same thing on our test drives. My friend also tried explaining to me why my car does that, and why my car doesn't get that good of mpg's on my glides, but I didn't really catch all of it because I was driving. (My glides at 55-60 only get me about 130 mpg.)

I'm fairly new to the whole hypermiling deal and I plan to purchase a new car, but I still like learning about the car I have now. I'd appreciate any tips you're willing to share as well.

Thanks Guys.