MTH Premiere GP60 - "shudders" at low speed

make sure the motor screws to the trucks are tight! Check for rubbing tires or similar. Lube all wheels and pick-ups.

also for ideas:

https://ogrforum.com/...-low-speed-operation

Thanks Engineer Joe. I will give that a shot tonight and report back. 

So tonight I spent some time and took it apart. It seemed there was a lot of grease in the worm gear area so I used a q-tip and removed some. I also lubed axles etc. It seems to be a bit better, but still sticks. I took a video of it with the shell off so you can see the motor is running. If you look at the white speed tape you can see it periodically stop at low speed. When I turn them by hand there doesn’t appear to be any undue resistance or problems. I tightened up the trucks so I am at a loss as to what else could be the issue. Any ideas? 
Here is a link to the video: https://youtu.be/M3OT0XrxXnw

If it has very low mileage, it might smooth out as it breaks in.  Also check out this thread and this thread.

It's possible that you have a spacing issue with the tach sensor or you're having some sort of reading failure.  Make sure the sensor is between .8-1.0mm from the flywheel tape.  You could also have a flaky motor, I've seen that before.

One thing you can do is unplug the motors from the board and connect them directly to a variable DC power supply.  Try running them in the forward direction and varying the speed from low speed and up, see if you ever see the hesitation you speak of.  If not, it's likely a control loop issue.

@Gerhardt I just watched your video.  Please read the threads that I posted, especially the 2nd one.  If you're able to make it run smoothly at 2 mph you're lucky; I almost think this is too much to expect from locos with this design.

If you don't want to unplug the motors from the board as GRJ suggested, you could use DCS to turn speed control "off" for test purposes.  The loco will still run without closed-loop control.  It will be tough to throttle it down that slow, but you can see if the shuddering persists when you get near that speed, and report back with your findings.

Thanks for your info and advice. I couldn’t figure out how to turn off speed control with the remote and everything I found was for conventional operation online. I had to send in 2 other items to MTH repairman so I sent this one too. I have lots of other MTH locos that can crawl at that speed so something is not right. Also the noise it makes at that speed is concerning. Again thanks for your help! I will update when I hear back from the service guys what they find. 

Did you check the tach sensor spacing? Run the motors disconnected from the board on straight DC to verify they are smooth?

I did check the spacing and that didn’t change things. Running DC was above my knowledge base so I hadn’t tried that. I’ve shipped it to service so I will report back what they say to assist with anyone in future. Thanks