I couldn't tell you rpm at a given speed without knowing the exact tire size, or at least a rough idea of the tire diameter.
30 inch tires
60 mph at 3064 rpm
70 mph at 3575 rpm
32 inch tires
60 mph at 2873 rpm
70 mph at 3352 rpm
32 inch tires with typical 27%OD transmission
60 mph at 2097 rpm
I can't answer your weight pulling question. Old trucks used to work hard all the time. They just went slower when they worked. Local restrictions might dictate what a truck can and can't pull. Be sensible, stay out of the left lane and use common sense.
70 mph at 2447 rpm
