See the attachment for the wiring diagram.
Below is a link with info on how to test the overload.
How To Fix a Refrigerator - Appliance Repair Guide - ACME HOW TO.com
Short your meter leads together before testing it so you can see if the meter has a zero offset.
If there is some resistance then replace it.
This would cause a voltage drop across it when the compressor is on so that the compressor gets a lower voltage and that can cause it to overheat.
It does sound like the overload is doing it's job of stopping the compressor from running when it is too hot so if the overload is OK then all that is left is a bad compressor.
If your compressor uses a run capacitor then that may also be a problem but the parts breakdown does not show one so I doubt you have one.