I was just about to mention the fuel pump relays, but then re-read your post. Hmm... scratching my head here.
When you say you checked the OVP, what did you do. Mine was quite hot to the touch, so it was replaced. Not exactly expert troubleshooting, but it seemed to do the trick.
Makes sense to replace the injectors, but how many miles are on the car and how cold does it have to get to cause trouble?
This may sound overly simplistic, but did you test the battery and check the condition of the cables? Are the terminals clean etc??