Did you ensure that the gap was correct. You can't run the iridiums on the standard 0.7ish - they need 0.9 - 1mm to work properly.
I've had them on my Evo for six years with no problems. More info here:
http://www.ukmonster.co.uk/monster/s...72&postcount=4
http://www.ukmonster.co.uk/monster/s...2&postcount=12