It usually means that the internal seals and the valve body parts are getting worn and stiff. You might be able to get a little more life from the transmission by adding transmission conditioner to the fluid. Try something like "Trans-X", but understand that whatever you do, the transmission is about ready to leave you stranded.
A worn transmission gear can cause a Chevy Impala to whine when the gears change. A bad fan belt can also cause this.
The most common cause for a transmission not to change gears, is low transmission fluid. Check the transmission fluid and fill to the full line.
You probley installed the filter wrong. Remove the transmission pan and check the filter.
It should have a 6 speed Transmission.
In an automatic transmission this usually means the trany is low on fluid or the trany has internal problems.
It has 5 foreward gears and a lock up converter.
Did you use the right transmission fluid or did you forget to maintain your transmission otherwise, your gears are broken and needed to be replaced.. chances are you need a new transmission.
You have not pressed the Clutch peddle to change the gears!!
It's a transmission where the gears do not change themselves, but have to be changed with a gear shift and a clutch.
It's inside the transmission (between the engine and the gears).
Your Transmission Fluid is very dirty. Change it and flush it first.
Auto or standard?