[D13]

My 81 factory light 3/4 ton has 3.43's with no overdrive. My 99 weighs 5600# with me and no gas and has 3.43's with OD, running LT235/16/r78's. With an overdrive trans and a v8, 3.73's would probably be better. You can get away with less gears with a V8 and an auto due to torque multiplication in the converter for starting the load.

Best bet is to pick your tire and trans, then use an online calculator to find the gear. I like to run my stuff 17-1800 at 60mph, puts 72 right around 2000 rpm which should be in the good part of the torque curve. I don't tow a ton (mostly DD) and when I do I run in 3rd gear and keep the speeds low.