As carrybosse said, a level spot is best. However, I think you can get your setup close with your sloped driveway. Get the trailer so it is parallel to the slope of your driveway, then move the ball so it is ~1" higher. This should get you close.
However, you will need a flat area for setting the tension of the wdh. The slope will mess with your front end measurements unless it is a very gentle slope...
Oh, and your tongue weight is too low. You should have 10-12% of the total weight on the tongue. This could have been part of the issue when using your 1500, though I think you made the right move to get a heavier truck for pulling that much weight.