My '75 GMC has a TH350, 4.11 gears and stock height 31" tires (245/75R16). When I drove it to work this week I was running about 2700 rpm at 60 mph. This is not hard on an SBC 350 engine, but it gets fairly noisy in an old truck with very minimal sound insulation. I also have an old chain-driven transfer case generating noise right under my seat, so your 2WD truck should be a little quieter.
I'm going to replace the stock hood insulation blanket (mine fell apart) and also add insulation (dynamat, etc.) to the back wall of the truck behind the seat and to the inside of the doors to see if it helps. I already have full carpet with jute backing, but there is still a lot of bare metal in these old trucks.
Bottom line answer - 4.10 gears work fine and the rpm won't hurt the engine, but the higher rpm makes more noise and the truck sounds like its working a lot harder. This noise increase makes some folks uncomfortable if they are used to modern cars where you can cruise at 60 without any obvious engine noise.
Last edited by 75gmck25; 03-01-2012 at 05:59 AM.