I am just musing, because I don't know the answer on such limited information :-
Logic tells you that the system is loosing steps when moving to the right ( it cannot gain steps). I do not know what your steps per inch is set at, therefore it is difficult to follow that much further , other than to say 1/4 of an inch in 62.5 is 40 thou per inch - how many steps is that..
What if you start the tool on the left and move the whole 123 inches, and back - does it finish where it started.
Similarly, if you start the tool on the right and go 123 left and back does it return to where it started.
I assume you have measured the movement left and right to see if the table is travelling short in one direction. You can certainly measure to 1/4 inch with a tape measure.
Logic says that the table must stop short, and the most likely place is to the extreme right of travel - is there any movement past the 62.5 inch mark or are you approaching limits - I know you have cleaned it all, so you have thought of that.
I think you need to do a little bit more detective work to find where the movement is being lost, before we can point to a solution.
There is no limit on Mach 3 to my knowledge - certainly not in one direction only.