4.10s and 235/85/16, I am at 2300 RPM at 65, 2500 at 70. Still get 21+ mpg at 65. I know the sweet spot is supposed to be under 2000 RPM with diesels but mine is plenty efficient at 2300. The V design of this engine allows you to get more useable horsepower at a higher RPM than with an inline. A stock Cummins falls flat on it's face above 2700 RPM, whereas the power band on this truck can go to 3K and in some cases beyond.

 

I usually run at just over 2000. Mind you, I've got 37" tires, so my speedo is WAY off. when running stock tires and 4.10's I was running around 2500 @60 when I had 3.55's, around 2100. Same as Brownie. 5speed, so as someone pointed out, the OD is a little lower than the auto.

 

all torque is is a twisting force, nothing else... you can have boatloads of torque, but without rpm (aka no hp) the load will barely move, you won't be going more than a couple mph but damn you'll be making a crapload of torque... diesels outperform gas engines because of an indirect use of the torque that they produce... they outperform gas engines because of the EXTREMELY wide powerband.
simple as that, if you want a USABLE vehicle to tow with, you want lots of hp in a wide rpm range, hence why diesels rule the towing world! a gas engine can easily surpass a diesel vehicle in torque by using gearing (noone cares what an engine produces, peak hp/torque wise, since you can easily alter that with gearing) but it won't get there very quickly since it won't have any hp

 

Thanks everyone (I'm the OP on this thread). This is why I love forums like these. I learned a big chunk of the useful stuff I know about my Toyota 4X4 from an online forum years ago, and now that I've moved up to the big trucks, it's good to know there's a community like this to tap into.
Yes, thanks for reminding me about jacking up the back and turning the tire to count driveshaft revs. From the discussions that have gone on in this thread, I'm pretty sure I've got stock 4.10s in the truck. Higher revs don't bother me too much, because I don't put a lot of miles on the truck anyway, and the long trips I take will all be with a camper on the back...I bet it'll perform great with that big wind stopper up there!

Have a good one