If it has a open drive shaft you might have a few options,a late model 5 speed o/d trans or check with gear vendors or US gear and see if a o/d unit could be added to the back of your original trans. I know the gear vendors o/d units are not cheap,you would have to drive it alot to get back what it costs. The rearend center section might be able to be swaped with a newer one to get a better ratio,I know gas is getting expensive but that is not a truck that will get light truck gas mileage.
