I bought a new DC one last year and gave it a good run in on my club test track, where it ran nicely. Next time I tried to run it, it could hardly move, and I found that one of the universal joints on the motor was broken. I sent it back and it was returned with "two faulty drive shafts" replaced. I don't know if this was bad luck, or a known fault as both shafts were replaced. It doesn't need a lot of pulling power, even if they use the same chassis for DMU versions, so why didn't they fit a simple power bogie at one end? That would solve the high floor problem too. I'm thinking of converting it to DCC, so hopefully that's not the cause of your running problems!