The TX 66 and the Tx 68 are exactly the same machines except the 68 has an additional sideboard on the bin, has heavier final drives, a heavier four wheel drive if equipped and 30 or 50 hp more depending on the year of manufacturing. The 68 has a little slower gearing in the field and on the road due to the gearing of the heavier final drives. The Genesis engine is extremely fuel efficient and can run at about .6 gallons per acre depending on conditions. The Fiat engine is an extremely powererfull engine and will burn a little more than the Genesis will.