I have a 2004 Monte Carlo 3400 Als I believe and the transmission won't shift into gear after being on for a min...when I first turn it on it shifts fine. But after a moment of being on it makes a funny sucking or grinding noise and then won't go into gear...I was thinking tyranny flush but I was told not to due to the fact it could be bad. I was then told a filter change which I have never done at all. The fluid is very dark...can't afford a lot and its my family's only car. Can't anyone help?

 

A flush won't hurt it anymore.
If the juice is a dark brown you waited to long it should be changed and the color should be a Red clear color when done.
The trans fluid should be changed every 30 to 40 k at the minimum.