How's the radiator? Is it the correct radiator for the 440, and is it clean inside, or is there crud that might be restricting flow?

I had the same issues with my Cuda after rebuilding the 360 in it in 1995. The temp would slowly rise while cruising down the highway, and would level off and slowly drop at idle. I replaced the radiator with a new 2-core radiator, and that helped - I didn't have to pull over to let it cool anymore - but I was still on the ragged edge of overheating on the highway. About a year later, I had an accident that pushed the radiator into the fan, so I opted to upgrade to a 3-core radiator (and had it paid for by the other guys insurance), and I haven't had a cooling problem since.

By the way, I also have a Taurus fan - it seems like a good unit and moves a lot of air. With the 3-core radiator, though, it almost never comes on. I have it set to come on at about 200 - 205 degrees, and the only times it will come on is if I'm in stop and go traffic or idling for a while.