just curious what do you consider lugging? what rpms would you shift at to get the best mpg, power and engine life while running mostly empty (couple hundred pounds in cab and bed)?
Well, when I was turning wrenches at a bus co, the factory rep dropped by and explained it as thus: You can lug these things at ANY speed regardless of RPM or load. If you cannot accelerate to full RPM at 2/3 throttle, then you are lugging the thing. And that doesnt mean standing on it at 2/3 throttle till it slowly creaps up 5 rpm at a time, you have to use your head, it should accelerate at a *normal* rate, in other words, you could be spinning at 2500 and be lugging the thing
Now, all of this schmaltz aside, peak torque is around 1750, which is also around shift point.... under load , you can climb hard in that range even towing heavy , just so long as your not floorboarding it ( and it will pull REAL nice ( Ive found mine pulls best in between 1750 and 2200 ) as far as going down running empty, you just have to be mindful of your foot. I have a double OD and my RPMS can get down there pretty good, around 1200, but I keep a VERY light foot on itand if I hit a hill I pay very close attention as to how much fuel is going to it, at those rpms if at any point its to where I couldnt accelerate easily , I simply drop a gear and play it safe, and get the engine in the correct operating range for pulling there is no cast in stone number. The goal is simply to prevent undue loading .
When Im on back 2 lane roads, I cant even use 5th gear, its simply too high, I just keep my brownie in OD and use 4th and that works great ( 5 over it too high, the split at 4 over is perfect and saves having to shift to 5 direct and fight the curves and 4 over gets the engine in a better mileage range when going up and down and pulling out of curves )
Which brings to mind, lower rpms does not always equal better mileage. If the road you are on has a lot of ups and downs to where you are having to stuff your foot into it a lot in 5th gear to pull the hills, you may actually find that you will get BETTER fuel mileage on that stretch by letting the engine wind up a bit in 4th and not have to give it so much throttle to get over teh hills.