Well, I found the cause of the problem. Took out the motor assembly and disassembled until I found the cause of the impeller slipping.
Here are all the pieces
http//images.yuku.com/image/pjpeg/f1b16f591d4ac516db58305aa2cae1ae998afdc1.JPG

There is a white plastic tube that slides over the motor shaft. It has ridges inside that mate up with similar on the shaft, so when the shaft spins, so does the plastic sleeve. Well, the plastic piece cracked and is no longer tight enough to spin 1 for 1 with the shaft.

A bunch of pieces slide onto this white plastic sleeve, and finally the impeller piece at the end.
parts diagram does not show this important plastic sleeve, and I cannot find it looking part by part.

Any idea what part this is?
Plastic sleeve:
http//images.yuku.com/image/pjpeg/a74265956d1ee410c8a152dabc73bf8e5655b30b.jpg
Parts diagram:
http//images.yuku.com/image/pjpeg/e96269854c172431cb8162d52f5f12199ef1b98a.jpg