Why does my 2003 ford explorer overheat?

What is your question?

Cold weather here. After driving a few miles at 60 mph with 'cabin' heater full on the gauge for engine heat shoots up into the red. If I catch it in time (so I've really got my eye on the gauge) and I turn the 'cabin' heat off engine heat immediately drops to just a bit over half up. This is totally counter to what I'd expect. And yet I've observed this twice now. The first time, of course, I had no clue. The engine overheated and the coolant was all over the engine. A small ID hose had blown off of a hose barb of what appears to be a round manifold. I reconnected the hose with the clamp which was still good. I figured that hose was for interior heat. Had the rad flushed. And now begins to overheat with interior heat on max. What I have also noticed that if I keep the interior heat halfway or less there's no surge of engine heat for 20+ miles. I've not tried other higher settings for fear of stranding myself. Definitely not a blown head gasket. Would the flush have cleared all lines?

What makes this problem better or worse?

explained in text: What I have also noticed that if I keep the interior heat halfway or less there's no surge of engine heat for 20+ miles.

How long has your 2003 Ford Explorer had this problem?

a month