Good morning TraciK,
Here is what I use because my driveway slopes in not one direction, but two. Each leg is adjusted independently. As seen in the picture the difference in height is around 6-8" from front to back.
How I unload in my sloping driveway is as follows:
I first lower all the jacks, but don't let any touch the ground yet. I then lower the drivers side front jack to level the camper left to right. I then lower the passenger front jack so it is just touching and then I engage both front jacks to bring the camper to a level plane. I then extend the rear jacks so they are both just touching and then raise all four jacks until I can drive the truck out. I slide the base under and re-level all four corners of the base and lower the camper down to share the weight between the jacks and the base.
In regards to unloading in your sloped driveway, depending on the slope of course, I would build some ramps for the front castors of your dolly to sit on. The top of the ramp I think should have a pocket for the castor to nest into with a wheel chock on the downward side to prevent the castors from being able to roll out of the ramp pocket.
Hope this helps some,
WestCoast1969