I can't confidently tell you how to get back to froyo but if you can, here is the link that I used to root my Evo:
[ROOT] unrEVOked 3.21: one-click root for Froyo, no downgrading - xda-developers
My hardware version is 0003
Software number 3.29.651.5
It took me about 10 minutes to do it. I really haven't read alot about the different software versions, kernels, etc so just make sure you read everything if you decide to try it.