We were thinking alike! I couldn't believe I was so dumb as to forget about the ReizaCommon folder--the most likely source of a problem like this. So, I deleted it and replaced it with the contents from the Beta install. ...no effect
That was frustrating, so I decided to eliminate all tracks except for this one and Jacarapagua, which also has the same issue easily noticeable. ...no effect
Tehn I thought--see I was right all along that it was likely a car mod. So I eliminated all Vehicles (deleted entire folder) and kept only one (old Opala) transferred over from the Beta along with the loose files from the main directory. ...no effect
This is quite unbelievable. I think there is only one possibility left--the Shared folder.