I'm very curious what you are using for pickups on your new chassis. Conventional hard HO pickups usually do not work well on the type of power conductors used for 1/43rd scale track.
Could you show us some closeups of the chassis? (I can understand if you don't want to.)
I'd also like to see the chassis running without the traction magnet. Since you are using a can motor, there should be little to no magnetic downforce without the traction magnet, so it would be an authentic gravity car. But the lack of downforce could cause an issue with the pickup system -- either result in poor power pickup and/or lift the front wheels off the track.
Ed Bianchi