What is your current antifreeze-water ratio? It can easily be checked with one of those little floating ball testing tubes (the more balls that float = the better the protection in both hot and cold weather).
That may be off-base since the overheating has happened both before and after the service work, but it's something simple that can be checked and changed if it's the cause.
Clogged radiator/and or fins could also do it in addition to the water pump. I had mine flushed, it had some nasty stuff in there.
I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
Thomas Jefferson