How can I tell or figure out what ratio I have in the rear end of my D100? I doubt that it has the original rear end in it, but I do think it is a truck rear end. Davey

Look for a tag under one of the bolt heads, that will show the ratio.
If no tag, count the turns of the driveshaft per turns of the rear wheel.
Do you know if the truck has a limited slip type differentiial?
DD

also if you feel like changing the fluid most of the time it will be stamped on the side of the ring gear