I just got my first 263, also from side track, and have a similar issue. I have heard that these loco's should be able to pull long trains, but with anything more than about five cars behind it is slips alot. I am serious considering just going old school and adding extra weight. I have been running mine on gargraves track. I wipe the rails clean multiple times but the slipping persists with any thing approaching an impressive train. Mine sounds and looks wonderful, but the slipping is a disappointment. I was hoping to pull about (8) 2816 hoppers and a caboose if it could manage. ( using o-72 curves)
Also I have had trouble with the engine side of the "wireless" drawer bar not staying seated properly. I was think about back off the screw that holds it up and adding a washer between the drawbar and the screw head to hold it a little tighter.
John Z.