It might be the pelvis - sounds quite similar to chloe!!
my girl is also falling off of things and miscalculating jumps and areas, and I am sure that is due to the RTA she was involved in before I adopted her. I was told she had a fractured pelvis.
When I compare the way she walks to fonzie, it is certainly different, and her limp is a lot less noticable then it used to be.
When she first came home she tried to jump normally, and failed miserably. Would get almost to the top of the couter, grasp on for deal life, and then fall backwards - and a bit embarrassed about the whole thing. She used her nails and front paws for a lot of grasping and strength to pull her up.
She is better than she was, but to compensate for it, I have plenty of things where she can have minijumps to get to her final destination. (ie, chair out to reach the counter or table, coffee table to reach the TV etc).
She is also clumpsier after naps though! and, she spends most of her time laying on her back, but dont know if that is pelvis related? or, if she is just a strange one!