Chevrolet: 2001 impala temperature issues, shade tree mechanic, three notches

Question
I work on cars alot,(shade tree mechanic) but my wifes 2001 impala is killing me. Under warranty, we had the coolant sensor replaced twice (low coolant light kept appearing when at proper level). 10,000 miles out of warranty, the car overheated. I replaced the thermostat and changed radiator cap (used a cap off of a wrecked 3.8 pontiac). The car did great for another 5,000 miles. The car overheated again (not severely) so ended up replacing the intake gasket which was leaking. I'm pretty sure It's not the head gasket because there is no coolant in the oil and the exhaust is not being blasted into the coolant system (like it did on my dads 3.1 lumina). The car is back with temperature fluctuations (not overheating yet) and I am ready to pull my hair out ( and I have really nice hair). When driving the car and accelerate hard the temp goes up a notch or two on the guage. When sitting at a stop for a long period of time (two minutes or so) the temp will go up about three notches about the half way point and then the fans kick on. when we bought the car the guage was rock steady 2 notches below half. Now its all over the place. Car currently has 56,000 mi. Can you make this easier to comprehend? I would appreciate any advice you can give. Thanks

Answer
CHRIS :
 Hea - well  the first thing I would do is to put a presshure  test on the rad. and cooling system that should show you any trouble that you are having. and check for a soft rad. / cooling hose some times they will suck close when hot and it will over heat.and is the fan turning ok ?
and how is the oil and filter ,