Car goes sideways?

Road crown can cause it but also if the alignment isn't right it will do the same thing. Find a shop that will do a 4 wheel alignment. I'd be willing to say that they will have to shim the spring perch back on one side to get it right. I went thru the same thing with a 65 Barracuda years ago and it drove me nuts until I had an old time alignment guy look at it. Needed a 3/16 shim on the drivers side perch to get the rear end straight with the frame.