At lunch I went home and put her back together, but before I did, I did all of the following:
-disassembled the motor, and added a thrust washer to the brush plate end. This eliminated all but a tiny hair of the motor's back-and-forth backlash. It also perfectly aligned the armature laminations with the field laminations.
-spun each disconnected axle by hand but detected no binding.
-repacked the worm well with lubriplate white lithium grease.
-lubed the axle bushings again.
-reassembled all the rods and valve gear, placing a tiny dab of grease on all bearing surfaces.
-adjusted the motor set screw to provide the same gear backlash as my 736.
What I mean by the last one - These locomotives have a small set screw under the motor, between the mount screws. Instead of shimming the motor up and down, you turn the screw. The worm/worm wheel fit on this loco seemed tighter than most postwar locos, so I fiddled with it until I could spin the wheels by hand in both directions.
Still, it all made no difference. It just doesn't run well unless it's moving at a good clip. Creeping into a turn, it often will stop completely and even dumping full voltage into the track may not make it move!
