I have a BLI J Class with a Tsunami 'heavy' in it. It was jerky at low speeds, and I had CV2 set at zero.
I have learned that with CV2 at 0, put a single speed step on your throttle with the loco clear to run forward close to level for several feet on the rails.
Enter programming on the main, to CV209, and enter a value near 30. Then enter CV210 and enter a value just a bit higher, say 40. You should find that the mechansim smooths out quite a bit. If not, go back to 209 and double the value of 30 to 60, and do the same for 210. At some point your engine's drive should smooth out. Exit, and you should have your engine moving on speed step 1. If not, add 1 or more to the value already in CV2.
It seems involved, but once you do this you will never forget both the procedure and how useful it is. Worked like a hot damn for my slightly jerky and annoying J.