I am working on a neighbor's dryer. She is a single mom and I want to make sure I don't spend any extra money...

The problem: Her GE dryer stops running about every 10 minutes it also takes a long time to dry the clothes. It starts back up as soon as she notices it has stopped.

Steps taken so far:
1) I cleaned out the vents pipe and that did not help.
2) She ran the the dryer with the duct disconnected and it seemed to work fine. Not sure if it had clothes in it for that test.
3) I took the entire dryer apart and cleaned every spec of lint from the internal ductwork, motor, cabinet, filter, etc.

I suspect it is the motor, but not sure. If it is the motor, that is something that's affordable, but I don't want to put too much money experimenting on a 10 year old dryer. Thoughts?