The NC routs look different after importing them because they are using "Cutter-compensation", https://www.cnc.com/g40-g41-g42-cutter-compensation-gcodes/
FAB 3000 will not display the cutter compensation unless you place FAB 3000 in NC Editor mode (menu: Windows > NC Editor Mode).
Probably the easiest thing to do is export your NC Routs without compensation. During Rout Export, check the option "Remove Rout Compensation(s)". Here's more detailed information, https://support.numericalinnovations.com/support/discussions/topics/14000012789