The fast focus could be a red herring. As Ikka mentioned, difficulty reaching secure focus can be a sign of some sort of optical defect, some of which are hard to diagnose.
Try evaluating just one side of the binocular at a time using the same eye to look through each side(tripod mounting will make it easier). Defects like astigmatism, misalignment, pinching and excessive spherical aberration usually occur in only one side. Does the image look the same in both sides? If you are able to reach good focus in both barrels when using only one eye then the collimation between the barrels may be off or you may need to more carefully set the diopter adjustment or the IPD.
You can quickly check collimation by placing a distant horizontal line (building roof, etc.) across the center of the field. Slowly move your eyes away from the eyepieces until you see two small circles next to each other. Is the horizontal line at the same level in both circles? This isn't a complete test of collimation but if the lines are not level you know the collimation is off.