If you put a 10 ohm and 5 ohm resistor in parallel which resistor gets more current at a given voltage. There is a lot at play here. Once a motor starts turning and the engine moves the wheels on the non turning motor move but th worm gear doesn't. You now have some bind on the motor which means it needs even more current to start moving.
This is similar to what can happen on a Slaved diesel. Seems the E-8 are the most offending in this category. You have to clean both motor commutator and brushes with spray. Check the gear lash of the trucks, and lubricate properly to get them back in balance.
For the 2 PS-3 engines I saw this problem with the tach motor had a lower winding resistance then the non tach motor. You can measure and test all you want, in the end I put a replacement motor in for the tach motor and it was fixed. When the second engine came it I replace the tach motor first and it was fixed. G
