Gear Ratio Swap

[03BlkZ]

I have a 70 C-10 short bed that I assume has a dana 60 12 bolt. It was factory with 3.73 gearing and is also a 3 OTT truck. I am running 255/70 tires on my 15 inch rally wheels. Now that my restoration is complete I'm thinking I want to change the gear ration to maybe a 3.42 to help lower the RPMs the engine it turning on the highway. This is by no means a hot rod truck and it does fine around town and up to about 60 mph but the engine sounds like it's spinning pretty good. I don't have a tach so I'm really not sure. The question is how hard is it to swap the gearing to something like a 3.42. There are a lot of car shows I want to go to that are within driving distance but with that gearing I really don't like to get over 55. Some of these would require interstate highway driving and I don't feel safe doing that at 55 to 60. I prefer to drive my truck over trailering.