Mine does it as well, but more so in city driving. I believe a lot of it has to do with the fact it's s/c, so there is parasitic drag when not at freeway speeds. I drove about 70miles on the freeway, and used as much gas as driving around 20 in the city.. kid you not. So... I think your...
I just got a 99 Regal GS s/c 3800. I've never had a s/c motor before. What kind of maintenance should I do? Also, what are some good cheap mods to start with? How much HP can the stock motor and transmission handle when driven hard 50% of the time?