Overheating Problems

Before we went on a trip, the car was overheating to the point of the coolant
boiling (gurgling noise). So we had the water pump and timing belt replaced
by the mechanic, and said it was good to go. During the trip we overheated
again (and on a midwest highway in the middle of nowhere, no doubt). This
happened about 4 more times to and from our destination. Each time we
immediately stopped and let it cool for almost 2 hours. The coolant level was
good, and so was the oil. That was a few weeks ago. Yesterday I was idle at
a drive thru, and the gauge skyrockets and dings at me with the temp sign. I
cut the car off for a moment, thinking I'd need to pull over and wait for the
engine to cool off, but when I turned it back on, the temp was back to normal.
The heat gauge idles between C & H; is that normal?

Any ideas on exactly what is wrong with this? The mechanics where I live
are not very informative at all. Any help would be appreciated :)