M1009 (Blazers) had the 3.08's and a TH400 with 31" tires. Cruise rpm at 65 mph would be 2200 rpm or so and the mileage would be in the 17-19 range. The M1008 (K30) had 4.56 gears and ~31" tires with the TH400 as well. Cruise rpm at 60 mph would be a very loud 3000 rpm. Mileage on that would be 13-15.
The sweet spot for mileage with a 6.2 is ~1900-2100 rpm...much beyond that and mileage falls off a fair bit.
I can't really say as far as highway miles. We never really got the ones we used above 35MPH. Except for that occasional midnight high speed check. /forums/images/graemlins/shocked.gif The ones we had did have 3.08 gears in them, which seemed odd to me too, but it worked. It seemed like we could go about week before having to fill up. The Blazer had a 32 gallon tank. Pretty much all we did was drive around in circles, back and forth between building, and idle. Hope that helps a little. /forums/images/graemlins/tongue.gif
The 1 ton military trucks either have 4:10 or 4:56 gears in the last 8 of them that I baught the milage with the two that were in running condition always got better than 12 mpg and on highway one of them got 17 mpg with 35s on it. The one with 4:10 gears have all been the airforce crewcabs. I still havent picked my last green chevy out at base but it is a one ton dually so it might be different.. /forums/images/graemlins/crewcab.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/cool.gif