car question: any mechanics help me out

[IlliniLou]

alright i drive a 2000 Alero and has like 125K miles on it. mostly highway miles from driving to school. on a recent trip back home my car started overheating and i pulled over right before the needle got to the red line. it turns out i had to get a new water pump.
alright im making a long distance trip this weekend and ive kept an eye on the temp. ever since it happened. the needle is always at the half way point but sometimes it'll move higher, at what point should i really be worried about whether or not these people fixed my car for good? i really dont trust the people who worked on the car because i never actually got to talk to the people who worked on it. (it was taken to a dealership because the car is an Olds).
this is an important trip so i dont really wanna be stuck on the highwayand get the trip ruined.
As you can tell i dont know anything about cars so any help would be appreciated.