I would recomend a fresh rear tire and more seat time. It sounds more like either a bad tire or lack of experence than a bike issue. That said, my wife rides a KX105 (stroked 100) in tight woods. I added a 12oz stealhy flywheel weight. This made the hit less abrupt and it hooks up much better when accelerating out of tight slipery turns. I suspect that stealhy offroad has a weight for the RM too. I would think that 10-12oz would be about right. My sister races a KX107 (bored non-powervalved 100) in harescrambles. Her motor is ported, high comp etc with FMF exhaust and no additional flywheel weight. It hits pretty hard but she is very experenced and gets around quite well (she won the HS championship for our district). Amazingly, she does very very well on steep slipery hills, showing up the vet A guys in our club on a regular basis.
good luck