Go for it. I would probably go to 4-low instead of 4H (depending on the hill length and incline) simply for the reduced strain and to reduce the heat the transmission is going to create at slow speed. By going to 4L you are taking a lot of the load off of the engine and trans, less fluid coupling in the torque converter, and will result in a cooler transmission.
If you can't climb out, get a little run at it and/or bleed a little air out of the tires on the truck to increase traction.
The only times I've ever had traction issues on hard dirt was with an empty 24' gooseneck flatbed trying to get going on an incline, and when I had a 4-horse bumper pull full of firewood hooked to an empty truck.