When Lionel did the Legacy 3751, those were a good batch of fan motors. I have two Legacy 3751 and run the crap out of them with no issue. As a Lionel Tech, I know the time frame when questionable fan motors showed up and it was after the 3751 was done. The fan motors Lionel has today are decent.
If I had the TMCC unit still, I would do what laidoffsick did and put in GRJ parts, then the unit would be a great locomotive. I do not have one of Johns to check but the Legacy unit puts out all the smoke you would ever want. Both the TMCC and Legacy are good runners. The upside to the Legacy locomotive is it uses the newer and much better RCMC board system. No more modular boards.
On the 3751 TMCC I had, I pit two 16ohm MTH heaters in the smoke unit and it blasted smoke. Wired them together to show 8 ohms.