tom, you should always use the motion Gxx keyword before issuing a move, unless you’re 100% sure of the mode.
I would suggest you to read the RS 274 NGC GCode specification :
http://technisoftdirect.com/catalog/download/RS274NGC_3.pdf
Once you have a good understanding of GCode functionalities, you can try and use TinyG.
I’ve been using it for a while now, and didn’t notice major issues. What you are mentionning really are the basics of GCode… I would be surprising that those basics methods don’t works, regarding what I’ve been able to do with the board.
The only issue I’m having is small unexpected arcs. But I’m still trying to figure out the cause (TinyG, USB noise, so on…)