[big D]

OK, I completely disagree that its normal for the car to overheat slightly if the coolant system is working properly. Unless you're driving up long very steep stretches, or towing uphill, your needle should not be fluctuating above the half way point. A year 2000 vehicle is not old, and any car that age should warm up until the needle his the half way point then be nearly rock steady.

As others have already said, check your coolant level. Also, check if there are any wet spots in the engine compartment, especially around the water pump to see if you are loosing even small amounts of coolant. If you see the temp rise above the half way point, pull over and see if the pump sounds like its running right or if its making a grinding noise, or if you see steam in the engine compartment.

I would take the car back to the shop and tell them they didn't fix it right.