NJ-Vince

Hi Forum, I am new to this forum. I am an HO guy and recently rebuilt my layout from the 80's. Growing up my dad always loved LGB but we couldn't afford to run a layout of that scale. Within the past year, I have been going to auctions and am slowly buying LGB and G scale items to build a nice little layout hanging from the ceiling and maybe a 2nd. This year, I am using my 1st g scale train under my Christmas Tree. He is my question- I have a LGB 2028D loco and tender mad win Germany which I got at an auction but was hardly used if at all. Underneath is very clean. I am using a Chicago Model International 20M The sounder as my transformer. It was also purchased used. Its a beautiful engine. But, it will run for about 5-6 revolutions around the tree and then stop. I cleaned the tracks but and am using a light on a wire checker and a volt meter and when it stops, I don't always feel like I am getting a good power signal when checked. I can't seem to figure out why it is stopping. Could the transformer not have enough power or tire out? Could my engine get too hot inside and stop to cool down? I don't ever smell anything like a burn or melted plastic. Since I am a rookie at this scale, I would appreciate any help you can give me. Thanks, NJ-Vince