I had a '63 C10 for a long time. I drove it all over the Western United States. I had the 283 and started with the 2 speed Powerglide, but later upgraded to the TH-400. Final drive was still 1:1 on both. I had a 3.73:1 rear end. I got a lot of speeding tickets in that truck. It didn't mind the freeway one bit. I won't mention that time in 1981 on east bound I-70 headed out of Denver at well over 100mph. :-)
My current truck is a '62 C10. It started life with a 235, 3 speed, and a 3.90:1 rear end. I didn't know it then. When I got it, it had been converted to a later model 250, an SM420 4 speed (a factory option), and still had the 3.90:1 rear end. It would do 60mph comfortably, but any higher for anything other than short bursts just to pass was a struggle. After the 250 died, I dropped in a '63 327, but the rest was the same. No gear changes meant no change in speed, just more power to do it. Rebuilt the rear end and dropped in a set of 3.38:1 gears (a factory option) and it loves the freeway now. It doesn't have the same low end torque I had with the 3.90:1, but I have enough horsepower with the V8 to make up for that.
Bottom line is that these are old trucks. Expect that and you will love it. They can be set up to run the freeway, if you use the right parts. Even factory parts like mine. You don't have to get too crazy trying to make it into a Modern Freeway Cruiser. If that's what you want, go get one. These are old Farm Trucks, but can handle the freeway if needed.
