I have a 69 super sport convertible. I replaced the steering box(leaking)upper and lower control arms on both sides. from 0 to 50 drives just fine. 50 and above it tends to drift to the left and to the right almost uncontrollable. Alignment guys did not touch the rear end. Any ideas?

 

I dunno but I think I'd go to another front end shop and have it checked out.