Hello, I have a 1991 Lehmann 92677 Lake George and Boulder "Rocky" train set that I have used as a Christmas train since new. Always been a little under powered for the number of cars I would like to pull, so this year bought a used powered tender. Ran fine for a couple of weeks, but now - while the tender still works fine, the engine "pulses" as it runs. Like it is getting slow AC power. Checked the transformer with a multi meter and the output is clean with no obvious power pulses. And the tender runs smoothly by itself. Checked the "feet" that travel along the track, even took off the bottom cover and everything looks clean and see no corrosion or broken parts. Any ideas on how to trouble shoot this problem would be greatly appreciated.