I currently have 4 speed in my '77 and what I'm pretty sure is a 4.1 differential. I really want to lower the rpms when I'm going 60+. I've been researching on and off for a few months and am stuck on whether to swap the transmission or changing the differential ratio. Unfortunately, I've never done this before on an automobile, so I need some help or suggestions. For the record, this truck is just my fun weekend run about. No towing, no heavy loads. Option 1. Swap the transmission to a W58. I found a few at a junk yard. I see that I'll also need the bell housing and I may need to modify the cross brace and shifter position. What else? Is it as simple as getting the transmission, having it rebuilt and bolting it in? Will my existing clutch work? OR Option 2. My rear axle is already leaking a little fluid near the passenger side wheel. So, I'm going to pull it and have new seals pressed in. Why not just change the final gear ratio while it's out? I seen some suggestions going to a 3.42 or 3.08 gear ratio. Where can I find these gear sets? I can find sets larger than 4 for larger tires/offroading, but that's it. Thanks.