Sounds odd. If all that shit is working like it should I'd say, before you replace the box,to try and unplug the fan when the car starts to run like shit. It sounds like an electrical problem. I'm running all that 10 year old 95' shit in my car and the shit is so old and brittle. My experience with those relay boxes is that they work or they don't. Sounds like the fan motor is on it's way out.