First tank MPG

[HummerNewbie]

I had been averaging between high 12s and mid 13s with 90% or more city driving. On average the only highway miles I get is 3 miles each way to work but that hardly counts. I have done one fill up since breaking 5K miles and it was in the mid 14s. Not sure why I seem to get worse than most but I did start paying attention and usually don't go above 2,500 RPMs running around town so it isn't that I am gunning it all the time. It is getting better though.