sounds like a bad programing job or a bad o2 sensor to me. my 87 mustang with a 5.0 did the same thing to me and it was the o2 sensor... also you might want to change that fan to a switchable fan instead of sensor run, they're sposed to kick in at 195, but i went through 12 sensors from 5 different sources and they were all opening at 210.... which is a little hotter than you want that motor goin to