@Sams Trains- on another recent thread, it was pointed out that Lionel steam traction tires are very thick and can contribute to the symptoms you are experiencing. You can change to MTH tires which are thinner which may help as well.
If you happen to have a spare switch, lay the engine upside down in a cradle and run the switch over the wheels. Might give you a better look at what's binding.
I would agree with Trainmaster and Harmonyards that the gap in the frog needs to be widened.
Bob
