i got a 2004 450R....and every now and then....when i go to shift into a gear if im on the gas some what hard....it either goes into gear and pops out or just grinds and dont go in at all....but like i said this happens once in a blue moon....could it be that the trans fluid is low?...or maybe it just needs a trans flush so to speak or what?....any input would be great...and thanks

i hope your not talking about from neutral?