dm690

hi im buying a mack dm 20 yard with e7 300hp engine,T2070 transmission and 5.73. where the truck is goin to work in steep hills. with the gear ratio and tranmission will be be good enough to turn off from in stand still position loaded in a steep hill and have good reduction comming down hills or is it best to beef up the gears in the back? and if to beef them up what ratios will be best?