It could be something simple as a pulled muscle
but Lola was recently diagnosed with HD and had the same symptons as Dallas...a funny gait and her rear end waddled/swayed from side to side when she walked...it was more noticeable
after a long walk and she was lifting her right leg up for a couple of steps when running and then putting it back down...infrequent to start with but it became more often and she would lift her left leg up the same but not as often....she has mild HD ,worse in the right hip...she also went lame a couple of times ,first on her right leg and then her left....she was also very unsettled at night as though she couldnt get comfy and she had and still has a distinctive click in her hips when she lays down or gets up
Lolas back end seems to slope slightly as well and she doesnt like her rear legs being brushed
Lola also has a resistance to her right leg being extended
I think dogs have a high pain tolerance and it takes alot for them to show that they are in pain
and they do tend to compensate in the way they walk/run so it isnt so painful for them...hence the waddle and leg lifting
Hope the vet is able to get to the bottom of it