An overdrive transmission is a good option, then you can still use it like a truck, and travel a little faster when necessary too.

Check out the "Tons o' Fun" section for more ideas if you decide ring and pinion or a whole different rear axle is what you want.
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=postlist&Board=45&page=1

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-