driveshaft ?

3" will be good for 6000 at that length so if you have 1 in 3 diameter that'll work or the 3.5 shaft will be better.. So at this point weigh them and see which is lighter now.

Many mopar shafts have internal dampening (added useless weight) and are heavier then they need to be, a few pounds in the driveline is equal to 10 times that In carrying weight