I have 2 sets of Williams passenger cars from the 1990's that have never run well.  One is a 5 car aluminum SP Daylight set with 2 add-ons(7 cars in all).  The other is a 6 car GN heavyweight set.  I have tried a variety of lubricants to allow these to roll easier without success.  A steady Postwar Lionel Berkshire can barely pull 4 of these cars on a level track.  They were this way new out of the box and I have talked with others that share the same problem  Does anyone know what up with these or had success in improving these or something similar?  I'd be grateful for any helpful input.

                       Chris