[grcutter]

Check your ground, then I may run a hot feed direct from the battery and see if it makes any difference.

Thanks for the suggestion. The motor has two wires coming out of it that go to the relays. I think that the relays just switch the polarity on these two wires to change the direction. So I'm not sure where the ground actually is. I don't think that it is grounded through the motor housing. Do you know how this is grounded?

 

[grcutter]

I connected the battery directly to the motor and it was still slipping. I took apart the gear box and then the clutch. Turns out that the clutch is worn. It has worn grooves in between the pockets where the ball bearings reside.
For reference for others: The Resistance of the motor is about 0.4 Ohms +/- 0.1 Ohm. This makes sense since it is supposed to draw ~30A from 12v.

 

[grcutter]

Yawn, yet another member asking for help and we respond. Wouldn't it be nice if he could at least acknowledge?

Not sure if you are referring to me or not but I did solve this problem by replacing the motor clutch which was identified as the source of the problem in post #3.
For reference here, the JD clutch part number is AM131230.
This does appear to be more expensive than some of the non-JD actuators but looking at the specs of some of these non-JD actuators, I see some differences in stroke length, weight ratings, and as you mentioned, rate of lift.

For those of you that do go the route of replacing the clutch, be sure to disassemble and make sure that the seals are reusable first.
The seal kit is AN272706 and can add a lot to the cost of this repair.

Sorry, I didn't take pictures of the worn clutch showing the grooves that formed between the ball bearing pockets.