Very unlikely, if your motors were not tuned it would mean you would miss steps all the time due to accel being too fast, it would happen the faster you went rather than the slower. Poor resolution could make motors jerky at very slow speeds but unless your ballscrews have a huge pitch thats not it.
You say wizards are fine then it cant be motor tuning as wizards just produce code, sounds like it may be your code, especially when you say it jerks round corners. That sounds like your code is made up of lots and lots of tiny lines instead of arcs, you could try G64 (Constant Velocity) if you are not already in that mode.
G61 is Exact Stop and if that is in your code it will slow and stop at every line before it starts the next which will give you jerky movement if your code is bad (lots of small lines rather than arcs)
Hood