gearing issue

[dammitmitchell]

hey all i need a reccmendation and preffered place to buy new gearf for my 83
i have 14 SF from an 84 diesel
so i think the gear ration is high threes but i cant remember the damnned tooth count but it's the small ring gear for it also 9in and some change
but yeah when i hit 4th gear (manual) it wont even get close to the power band and it eats a buttload mroe gas then the old 10 bolt did (no idea what the gear ratio was because the ring gear was in iddity bitty peices)
so any help advice so i dotn order the wrong one??p.s. is it reccomended to put a posi in it?
i'll answer question yall have
thanks you