Thanks creek side. It wasn't the door as I could open and close it easily with one hand with no binding. I took down the motor unit and brought it inside to my work bench, tore it apart screw by screw and connector by connector, and gave it a good cleaning. Put it back together and hooked everything up - works perfectly now! I think it must have been oxidation on some of the internal connectors, or it could just be that taking everything down loosened up something that may have been binding a little on the screw drive. Now I'll just have to wait to see how it works in the summer...

This is generally caused by a bad bearing letting the sprocket lean forward and the chain jumps off. You can get the part at Sears or any opener service company. It is called a Gear and Sprocket assembly and the part number is 41C4220A. It should also come with instructions.

Make sure when you are programming the remotes that you release the smart/learn button quickly. If not you will erase what you have just done. What I normally do is hold the button down on the remote and then press and immediately release the smart/learn button. If this isn't the case then I think you have a bad logic board. I tried looking up the model numbers you give to make sure the remotes are correct but Sears doesn't recognize either model number.

You could have a bad logic board or bad motor. I would think logic board.