Sounds like you've got 2 seperate problems. For one, it does sound as if the IMRC box is not opening the secondaries. That would explain the loss of power above 3500rpms, and the "chugging" in 4th gear. As for the car dieing when coming to a stop, could be a number of things. We could use some more info about the car. How many miles, what kind of maintenance has been performed, what year/model?
Mark
