You need to get back into the tilt cylinders and find which one has the defect.
I agree that the problem may be in the cylinder having the lesser amount of travel on tilt back.
Just a bit of speculation on my part but the unequal travel could be because the piston retention nut is loosening on the cylinder rod. That theory would also account for the excessive drift forward because the oil is bypassing the piston in the piston center bore (not past the piston circumference seal ring).