Model 17 RES spec#GM51561-GAI serial #2234881 - purchased 12-10-08 - the engine loads down and turns off before finished charging - and it does it with breaker on or off and it is intermittent - does not do it all of the time

If the unit 'loads down" with the breaker off as you indicated, it isn't the load, (unless someone has wired it on the wrong side of the breaker to the home) and is been overloaded. Assuming that is NOT the case you need to check the stator wires to the breaker for ground shorts, especially when the unit warms up. I had a case once where a unit had a bad stator, it would run fine then as it was put under a mild load it would just bog down like overloaded, the stator was heating up and causing a ground fault. Have the unit load bank tested also. I am interested to know what you found?