I don't know for sure about 1688 series, but there was a huge difference between fuel consumption going from 1680 to 2188. I would consistently run along side 2188 with my 1680-when he went to fill up I would still have several hours of fuel left. This has been common complaint with many 21 and 23 seies owners in my area. as for unloading time, you definitely have a problem-it should not take nearly that long to unload. I have had experience with 1480,1680,2188,and 2366 -none of them had that prolbem even in 200 bu. corn.