Eddie,
We have a 2004 38' DSO4 with 4 slides, so it's a very similar coach. First, you should have a white label on the left wall very close to the back of the driver's chair. If it's there, it will have the correct tire size and inflation for your coach.
If the label isn't there, I will tell you that our coach has 275/80R/22.5 tires. Apparently this is a size exclusive to Michelin, which was what our coach came with. When I've replaced tires, Michelin was the only brand I could find in that size, which is okay with me because I really like their tires.
Hope this helps.
Lee Ensminger