Worked on it for a few hours today.
All of the running gear seems to roll smoothly without the motor, but... stay tuned.
The worm gear and the worm wheel are clean and free from burrs and in alignment and newly greased.
I do not have a precision power supply. Was going to buy one, but then the bad reviews on the Chinese one some months ago stopped me. Using a Lionel HO power pack that does not like to hit 10 volts. 9.5 yes, and 11.5 yes.
When free running, removed from the chassis, the RS-385PH motors read out as follows with no load:
Weaver motor 190ma - 210 ma at close to 10 volts
Lionel 160ma at close to 10 volts
MTH 160 ma at close to 10 volts
All three motors have similar torque values while being stalled by my admittedly uncalibrated hand. The Weaver motor has more end play than the others by a factor of 2.
Too bad the Weaver worm has a coarser thread than MTH or Lionel, but has a finer thread than K-Line.
On rollers, the loco will run slowly at around 2.5 vols and around 600 ma, with smoke unit off, but still clacks and bucks.
Thought the smoke piston was problematic. Relieved the push rod with a grinder where it looked like it was touching the smoke unit and also removed the O-ring around the piston. Made a slight improvement, but did not solve the problem.
The third set of drivers is connected to the gear box. Upon close visual inspection, it appears that this third set of drivers might be slightly out of quarter by only a few degrees on the right side of the loco. When running with the motor, the loco clacks on the rollers as the sound is coupled to the bench and the fiberglass lunch tray on which the loco, track, and rollers sit. Rotating the flywheel by hand, there is slightly more physical resistance at one point in the driver's rotation and at that point, the side rods between the second, third, and fourth set of drivers get tighter on the right side of the loco.
So it looks like I will have to send it to someone who can re-quarter the third set of drivers.
Thanks for all the help and ideas so far. 
