Well p.j., starting with the rear axle in you truck. First a two speed axle has a low ratio of 8.72 to 1 and a high of 6.4 to 1 the high ratio being the same or near the same as you stock rear doesn’t get you anywhere. Gear sets for the old axles come in come in one ratio the one you have so that is out.
So this brings down to 4 options when looking for more road speed.
1 change the rear axle for a later model rear with a taller gear set or with optional gear ratios
2 swap your transmission for one with an over drive.
3 install an aftermarket overdrive unit (i.e. Gearvender) behind you existing transmission.
4 use taller tires.
Now for the pros and cons
Changing the rear axle pros
1 may be the easiest if you can find a suitable axle.
Things that make a suitable axle 1 track width. 2 spring perch spacing. 3 perch width or the width of the springs that it was mounted to. 4 Dose it use the same wheels? If not you may want to change both axles. And 5 don't forget dose it have the gears you want.
2 you may kill multiple birds with one stone like improved late modal brakes. Parts that are more available should you break your new rear. Of course this all depends on your choice of a replacement axle.
Cons would be finding a suitable axle.
2 swap you transmission for one with an overdrive.
Pros will not hurt your low end pulling power.
It can be easy to do.
Sorry my short attention span is getting to me I'll have Finnish this later.
