[AtomicYJ]

I've driven my '83 K-10 across the country twice, once from Washington to Georgia as a 6.2 diesel SM465, and once as a 350 SM465 towing a trailer from Washington to Mississippi. I have a 33" tires and either 3.42 or 3.73 gears (can't remember, not near truck right now) and it did just fine going 70 the entire time except up mountain passes. Stock ratio should be 3.73 and I would leave it that way if you plan any towing.

Just my .02 cents