Transmission problem check engine light.

Hello again,
I'm not exactly sure if this is a transmission problem but I think it is. I'll tell you the symptoms. When I am driving the shifting works just fine sounds smooth and whatnot. The problem occurs when I drive about 4mph above the shift point (on 3rd 4th gear) completely let go of the accelerator and let it drop to near the shift point then apply the accelerator again. The transmission kind of clunks around like its not sure what gear to go into. Its almost like shifting between drive and neutral a bunch of times while driving. But this is 3 or 4 times in a second. And then it goes fine after a second. The check engine light came on once because it did it for a couple of seconds but it hasn't done that since. It only happens when I completely release the accelerator. This has been occuring for a couple of days. My fluid had little foam on the dipstick when I checked it so I'll just make sure there isn't anything in the fluid but would that cause the problem anyway?

Thanks so much for your help and opinions!

Problem Solved!!!!! Needed to adjust the throttle cable inbetween the throttle body and the transmission! Works great now.:sunglasse