Hi everyone!

I just bought a 03 4.4i and it has some transmission problems. The first thing I noticed was that when driving at steady speed around 50mph the rpm slightly fluctuates. This doesn't happen when driving steady but faster 70 - 80mph.

Then I realized that when driving around town, it shakes when changing from 3rd to 4th almost always. It goes away if I press the gas or if drived in manual mode. When happens it feels like driving through a bumby road.

Do you have any idea how can I Fix this problem?

Thanks!