Thank you for your work on this. I have been trying to see the limousine in this clip for years and years (since 1983, when I bought a set of WFAA VHS tapes) and never could find anything . No wonder! They're not going up the hill, they're going sideways across the screen!! Bert Shipp narrating the film said they're "going up the hill" so that where my attention was drawn to. Thanks a ton!!!!
Also, the Johnson car and his SS car must have gone over the set of railroad tracks at the top of the hill! H.B. McLain stated that he "Almost lost it" (his motorcycle) when he flew over the tracks.
James Courson gave this account in "No More Silence."
"Just before we reached Harry Hines Boulevard there was a railroad track on a small incline. All the motorcycles left the ground at the same time, and it appeared that the wheels of the limousine came off the ground as well. Of course, the driver was doing all he could to handle the car after jumping the track and then preparing to make the sharp *left* turn onto Harry Hines."
A "sharp left turn"? Sure looks like it turned to the right after going over the tracks.
Courson said he was located behind the limo on Houston Street during the shooting but then raced up and caught up with it as it entered/turned onto the Stemmons Freeway ramp.