I have a 1994 American Eagle on a Sparton chassis. The 6 speed allison goes down the road nicly but when trying to go from reverse to forward or the other way, sometimes it will not shift. If I turn off the rig and restart it then it will shift. The RPM of the 300 HP Cummins is at 700 RPM. The unit has been sitting for the last 3 years with regular exercising of it except in the winter. Does anyone have any ideas of what to look at.