MTH Premier F3 and Ralking NW2 "Lurching"???

If you could include part numbers for the engines that does help with some of the troubleshooting.  I'm going to assume that these are PS2 or PS3 engines and the rear motors on both engines have tach tape on the flywheel and a tach reader.

The behavior you describe above is normal for low speeds (1 - 3 SMPH). The PS2/3 board will apply voltage to both motors to reach the desired speed as indicated by only the rear motor.  If the front motor doesn't start moving by 5 SMPH, then I'd investigate the motors more.  One (or both) could be bad. I'd also look to make sure there is no binding in either of the truck gearing.

Sorry, should include in all my posts that I'm using BPRC, no longer using DCS.

Let's just say I have 0-9.6v going to the motors, what would cause the rear motor on each diesel to start before the front one?  No mechanical binding that I can tell.  I'm thinking it's nothing more than the motors are not "matched" or in sync.  When assembled I'm sure they just grab 2 motors out of the bin and put them in.

Check the current draw of each motor with no load at the same voltage. If the draw is significantly different then yes it one has less resistance than the other.  What is your system using for speed/cruise control or is that not present? If it is only monitoring one motor's back emf and feeding voltage based on that could explain the lurching.

I'm using a Deltang RX65b receiver.  I've posted on another forum to see what they say about how it handles 2 motors.

I MAY have found the problem...While I had the F3 apart I decided to clean out the old grease on the worm and gearing.  I say old, not sure how old the unit is.

After cleaning it out and making sure there was no debris in the worm/gears I re-greased and gave it a spin.  I can still see the rear truck move just before the front truck but it has drastically reduced, enough that I'm satisfied with it's performance as of now.

Makes me want to do that to all my diesels although these 2 are the only ones giving this problem.

I did not see any big debris in the grease I removed, but I did find out one thing...grease and cat hair are a no-no!!!  That's some fine cat hair but it may have been enough to gunk up the works, mini hairballs!!!