Re: Herky jerky slow speed cruising?
Adding a larger rear sprocket will lower the speed at which you can still cruise comfortably, but you will lose top speed.
I'd suggest a 50 tooth for good 10mph cruising, but don't expect to break 20-25mph.
A shift kit will give you both worlds at a cost of course....
If more is better, then too much is just enough.
If you can't afford it, build it yourself.