2 part question 1) Check gauges 2) coolant

Hi everyone. I bought this truck new. I have had it serviced by the dealership
when needed. About 4 years while driving on the highway i narrowly avoided
some debris falling off a a vehicle in front of me. I hear something bang
under my truck as I drove and then later when I exited the highway and
slowed to a stop i momentarily lost power and the check gauge light came
on. I got "her" to the service department. They couldn't find anything wrong
and she ran fine for a few months then the same issue. It keeps rearing its
head every 6 months or so. Any idea of what could have been affected?

In the last 2month I had my water pump replaced becuase I was losing
coolant.  Yesterday I was driving and the check gauge light binged - i
noticed that the temperature gauge was low - only about 1/4 of the way up.
It usually stays at a little shy of half. So I popped the hood and saw that the
coolant was just below minimum. I added coolant and drove it home and let
it sit overnight. ( the temp gauge stayed low and did not get up over 1/4 of
the way) I checked it today and it was a bit above min. Any ideas of what
might be going on?