[1969 GMC]

is your truck an original Big Block euipped truck?

if so, they had 3.54 gears in the dana 60 factory. otherwise, they should have 4.11 gears in a 3/4 ton. i am not sure if the 4.56 came in the dana 60 rearend, perhaps as an option. I am not sure about the gearsets you could get, I am guessing you have a 3-series carrier that will hold all 3:_ _ gears. maybe someone else can help.