I think it has something to do with Evo Design phones that are at least a few months old.
My Evo took the ICS, and it was so laggy and basically useless that I took it back to Sprint. It was totally stock, had not been rooted, and was purchased in April of 2012. They ran some tests and the phone failed several categories. 2 days later I have a new Evo Design running ICS just fine. I did just root the new phone...just because.....
I noticed the hardware rev on the new one is 002, while the old was 001...... dunno if that has something to do with it, but my gut says there is an issue with many older Evo Design phones. I'm keeping mine because it is brand new and was a free replacement; but after 3 HTCs......I might try a Samsung next...if they weren't so damn huge. I'm one of those standouts who prefers a smaller device....
If your phone is still under warranty, has not been rooted and has a locked bootloader, I would be real tempted to take it in and have them run some tests. You might just get a new phone out of it.