So I installed the solid state reversing unit (12A model from Dallee Electronics) into that 4866 GG-1. Low speed smoothness improved somewhat and the Pullmor grind and e-unit clang are gone (kinda miss 'em if I'm honest). The motors are definitely more powerful - under pull test I now get moderate wheel spin (where as with AC power the wheels barely turned) and it now pulls at ~4 lbs. The motors also run cooler. The only two steps from here are more voltage or steeper gearing. Neither is easy so I'll probably leave it there.
Hello SAL9000.........
Of course the AC pullmore motors are more powerful is because the armature of the motor is nearly same size as the WHOLE DC can motor is. Check it out by having a pullmore AC motor armature and sat it side by side to the DC can motor and you will see, no doubt about it smile. I know because I had a Williams GG1 which had DC can motors and older lionel LTI era GG1 AC motors and saw the differences between them 
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Tiffany
Actually, in general terms a DC motor is going to be more powerful per unit of size vs. a universal motor as it uses magnets. Quality of magnets, windings and insulation (higher quality = more flux/current = more torque) is a factor too. The issue with models trains is many use cheap DC motors made for pennies. They seem to get the job done as not many owners to complain about lack of pulling power in modern trains so I don't fault manufacturers. Even the testing I'm doing now with ~30 heavy postwar cars the GG-1 is only ~60% taxed and pulls all those cars fine - the problem now is couplers popping and cars tramlining.
