What are the common signs of a failing ECU?

A failing ECU can produce many different symptoms, from a inoperative running light bulb to a hard misfire that your experiencing. Our tests would include isolating the issue, starting with the basics (some of which it sounds like you've already tested) all the way down to particular input and output circuits at the ECU. What type of misfire (single cylinder, multi cylinder, inconsistent, specific, random, etc.) would determine what type of testing is necessary. Have you had any progress on the issue in the last 4 months?