On hills with extreme uphill angles and soft dry ground, you are going to have problems climbing no matter what you change. You have to remember that you are riding one of the most powerful dirtbikes available, so your riding style will need to be changed. On those loose uphills, you will often need to climb the hill with a controlled slide. By that, I mean that your 500 is going to drive up the hill a little sideways. It may even want to switch sides a time or two. Don't worry, you'll get used to it.
As a note, I agree on jetting. Power delivery that is not smooth with cause your rear wheel to break loose after a slight boog in power. However, even with this spot on, you will still have to change your mindset on the 500.
Most folks are affraid of the power of the 500, and rarely take me up on my offer to allow them to take a quick ride. Except for my 15 year old (who has been riding my 500 since he was 13), I don't think anyone else has ever ridden my 2002.
Enjoy the power, but take your time getting the feel of the bike.
Rick