how big are the spacers?
and why is your back end saging if the spacers are the same hight?
i have 31"mtrs on my gv and didnt do any cuting. i only rub at full crank on the frame rail.... with a 2" body lift, and what i call a 3" susp lift but i only used a 1.5" spacer in the front,
you should fit 30's just fine...... even more so with your front bumper cover off....
-Lance