Yikes. Have you cleaned the tires to ensure there is no slippery contaminant on them? It might be worth using some Goof Off or similar product, maybe lacquer thinner, to remove any factory coating or some other crud that is there. It might be worth setting the locomotive on a sheet of glass or a mirror and seeing if the trucks all sit flush...all eight/twelve flanges making solid contact. Failing that...there's always Bull Frog Snot. Works for me.
FWIW, I have a seven year old Gold Train Master H24-66 that is a superb locomotive. It's the only Atlas loco I have, being a steam guy, but I am very impressed with its quality and running qualities. It is very surefooted and used to take 12-15 hoppers up my 3.5% grade quite handily.