If you come up this way, the Alberton Gorge has some really great III's with a couple of IV- rapids.
The Yankee Jim Canyon section of the Yellowstone (just north of Gardiner) has some III's that can get pretty burly, depending on flows--but its a short run, so if you travel there, make plans to lap it.
The Gallatin has an awesome III+ stretch called the Mad Mile.
Are you down in S. Idaho near the Payettes? I'd love to hit some of those waters one day.
Hit the III's, play every wave and just go crazy. When you can play on all the tougher lines in a III, you're ready to stay upright and just "survive" in a IV. I'm just starting to play IV's. V's scare me. :laughing: