Runnin out of transmission fluid in f350?

well you obviously have a transmission leak

look under car to find out where

could also have a bad torque converter that is sucking fluid ,but this also will leak somewhere as it over fills

a good indication is look where the oil starts on under side of car

if at front of transmission could be torque converter or front seal

could be as simple as pan gasket

if oil starts at rear of transmission look at rear seal

rear seal is the easiest and cheapest fix

hope that's all it is