Is it a one ton? (3800)? or a 1.5/2-ton? (4000 or 6000-series truck*)?
If it's a 1-ton, you're in luck!
Read This It's so easy, even I can do it (and I have ...

) Yah, sure, you can do the 5-speed tranny thing ... and deal with bellhousing adapters, cross members, blah blah blah. But with the rear axle third member swap, all you do is remove one and replace it with the other -- all you need to do is find one
If it's a 4000 or 6000 series truck (1.5 or a 2-ton), well .... I am not eager to disagree with Brother Pruss, but ... I must. (sorry Ed) ... You are simply out of Schlitz on that one unless you want to upgrade the engine. On the bigger truck, the 216 is simply not enough engine to push that weight around very fast no matter what gearing or brownie box you slap to it. Unless you live on flat ground and you like shifting ... a LOT.

No matter what, though, if you do get the truck to cruise faster, please also go through your braking system and your steering. You can safely cruise the 1-tons at modern road speeds with just the rear pumpkin swap, but you *must* have good steering and brakes to be safe.

*If it was a COE/5000 series truck, I assume you would have made a point of saying so -- most COE owners do ...
