[Avocet]

120 miles on a tank does seem quite low. I had a 2007 GS, which I think is the same as your 2006 bike. If I remember correctly I used to get around 200 miles on a tank and still had some range left to look for a gas station. The only exception to that was when I was heading into strong headwinds while traveling at 85 mph on a ride across South Dakota one year, but I think that only brought my range down to maybe 140 miles or so (it was several years ago so I'm not sure I remember accurately).

May I ask how much gas fits in your tank when you fill it after riding for 120 miles? I'm wondering if your fuel gauge is inaccurate and telling you to fill up before you really need to do so.