My truck tends to stay at full a long time, then drop to "E" pretty fast. When I am at around 1/4 tank, and fill up, I generally still have about 4 gallons left in the tank.

I'm not too sure that the measurements that came with those gauge senders were terribly accurate, but then again, I've never wanted to pull the tank and experiment either. Just about every MV, I've ever owned or had much time with had pretty much the same fuel gauge. It was more of a suggestion than anything.

Coming from motorcycle world where fuel gauges weren't the norm up until very recently, I have learned to know my vehicle very well and either gauge my fuel with the odometer or the suggestive fuel gauge.