How do I even out a tile floor to properly support a dishwasher?
"Most" kitchen appliances have adjustable feet that "should" be able to adjust to take up a 2-3" difference in flooring heights.  Your other option is to measure the difference and fill the gap with an appropriately width piece of plywood.

Check out this Image I found on http://www.dannylipford.com/how-to-install-a-dishwasher/