How hard is it on the drivetrain (tranny, rear end etc...) to back a 10,000 pound trailer up a fairly steep hill? Should I use 4 high or 4 low? The hill is hard packed dirt so traction is not too much of an issue in 4wd but I am worried about the transmission and diffs. I know the strain is much harder in reverse than forward. I drive forward up hills like this all the time with a heavy trailer with no problem.

Oh, the truck is a 2004 f250 crew cab 4wd... 6.0psd and torqueshift auto with LSD rear end.

 

I do the same with a bit more on the weight...like 3k...and have no problem.
I keep squeezing the throttle untill it builds boost and then roll off ..as it gets going. Easy on the loud pedal
I have 4:11 gears

 

Not being an expert on the Torqueshift transmission, can we assume that reverse and first gear share many components much like other transmission designs? So, I don't think there'd be a problem. Personally, if I were backing that amount of weight up a 10% grade or better, I'd use low range. That just makes it easier on the transmission. As for the differentials, actually the cut of the gear teeth makes the mesh of the teeth stronger in reverse. Axle splines are the same cut on both sides, so I wouldn't anticipate an issue there either. Your limited slip helps, but if the hill has a sharp turn, remember that the front of the truck backing up hill will have (hopefully) equal traction on both front wheels and also have an added amount of weight transfer plus the engine's weight. If there is a turn on the non paved roadway, you could experience some wheel hop or traction loss at one wheel if you turn too sharply. This is because the spider gears will only allow for a small amount of differentiation in the turn. As things bind, something has to give. Better to be a bit of traction than an internal part. I would not unlock hubs and use low range in reverse with that amount of weight. This could damage other components.

I'd go slow and easy in low range 4x4 with a moderate to heavy load on a steep incline in reverse.

 

I've been told by tranny machanics that more damage is done in reverse than maybe any other gear. That is one big advantage of a 4 X 4. IMO put it in low range to back heavy loads up a steep grade.

 

Have you seee the commercial with the 05 Ford pulling that MAX load......It's going backwards....Good Luck