I’ve been experiencing this issue for a few days now, primarily in the Borderlands but also in Tyria though not as consistently.
While running it will appear that my character is moving slightly slower than normal, then after a couple of seconds it will appear to speed up to compensate. Once the slow/fast waves begin there is no point at which it looks as though my character is moving at the correct speed. Running alongside other characters there seems no loss or gain of net speed, it’s just a bit disorientating. One thing it seriously impacts is jumping, I’m missing even simple jumps because I can’t judge where my character should be when I hit the jump button.