Hey Gary,
Yes, the tires are at least partially fluid filled. Previous owner didn't know how much, though. Are there recommendations for how much liquid? I suppose I could find that somewhere here on the forums.
The skidding on the hill I mentioned was before the box blade, and the extra 450lb on the back does help a lot. I've got plenty of concrete blocks and bricks around, so I can try loading it up more.
I wonder how this will affect box blade operation? I have been going back and forth between FEL and blade, scraping up 3-4 boxfuls, then loading it off to a big pile on the side, or hauling it off to a low spot I'm filling in another part of the yard. So I wouldn't want to be swapping blocks on and off all the time.
Hopefully more weight would help dig in the tough spots, but I could angle the blade back for other areas so it doesn't dig down too quickly.