FYI Fred-The later versions of the loco indeed came with lower geared trucks and correct wheel flanges, my three are built like tanks and probably some of the better designed and engineered locos out there, there is a definite gear change that occurring sometime between AHM and Rivarossi, the only reason I know this was an attempt to repair a truck using an old AHM loco bought off Ebay.
The only downside to these locos I have experienced is the bolts holding the side rods on can become loose and fall out, so be sure to check them regularly.
I forgot to add a link to the TCS website that shows instructions on adding a decoder, in the process it shows how to disassemble the loco, at least down to the frame, which can be the most difficult to figure out, after that is pretty self explanatory. Beware of removing the V-Cylinder assembly unless absolutley required, it can be a test of your patience putting it back together.