Ford F150 - Side window trouble

When I roll up my passenger side front window in my 01 f150 4.6 2wd, the window will start off fast, then it gets really slow in the middle and then speeds up the rest of the way until closed. Whats going on with that? Any ideas?
Thanks in advance!
Adam

The glass run (felt channel) may be pinched, kinked, or dry, or the regulator slide channel riveted to the glass might be dirty or dry. Pull your door panel & inspect, using a flashlight & mirror if necessary. It's vaguely similar to these diagrams.

I just checked it out and found the problem. The felt "channel inside the door, which the rear of the window slides against, had come loose from where it clips to the inside