This is the steps you should take:
Flash-->hard reset (this is automatic by RUU)-->let customizations run-->hard reset again.
The rationale behind this is that a hard reset doesn't reset EVERYTHING. But a reflash is a complete repaving of the phone. There are some things that get done to the phone by customizations that are nessecary. The contents of the ExtROM aren't all junk...
Like I stated above, once you run the cusomizations once, then you can hard reset. That will blow out all the BS Sprints puts on but lower level configs that get made are unaffected by a hard boot.
Make sense?