Transmission Slipping

My car is idling at around 600 rpm’s which seems a
bit low. When I start accelerating I will almost need
to floor it in order for it to catch the next gear.
Sometimes even a gradual acceleration and then a
little harder of a tap on the gas pedal will get it to
catch. Then as I let go of the gas pedal, it will run at
1000 rpm’s while maintaining speed down the road
almost as if I were using cruise control. This is while
staying off the accelerator the entire time. I have no
clue what is going on... please help!