I've got the same problem with my 06 Heritage. I'll do around 155-165 on my 5 gallon tank (putting in around 4.5 gallons), but the light comes on around 70 miles, and the gauge seems to match that. I took it in, and they said they "adjusted" it, and it will be fine now. Well of course it isn't. Nothing's changed. AND, if I remember right from the self-help tips, there really isn't any adjustment. You can try bending the sending unit and really messing it up, or you can replace it. That's my next trip to the dealer.