I thought somebody might have an answer to why I can never get more than 16-17 gallons into a tank that is listed as having a capacity of 21 gallons even when trying to "top it off" (something I know one should not do). It is also odd since the first year of operation and driving under the same circumstances this never happened. I drive on California freeways where it is not uncommon to have exits 20-30 miles apart. I also sit for an hour unexpectedly at bridges and toll plazas. Therein lies the problem of unintentionally "pushing the limit" of the tank. It just seems the reserve light comes on too soon (not even near the red zone). I would think that the calibration or sensor might be off were it not for that nagging question of where the remaining 5 gallons have gone! I realize that letting any tank get low risks getting sludge into the fuel filter, but now I have no accurate way of knowing when that will be likely to occur. Thanks for anybody who has had similar experiences.