What Ed is saying is, get both back tire off the ground and fill the tranny with diesel. The side plug is your fill level.
Run the truck in second gear for a minute or two. Drain and fill with 90 weight gear oil till it starts to come out the side plug.
The fill level does seem low, but it get the lower gears in the lube and splashes the rest of the gears and bearings for lubrication.
Don
