It could be that your seals inside your transmission are bad. Have you had your transmission fluid drained and re-filled and your filter changed? I'm not saying that that would fix your problem but it's a start. Also your gears are a set of gears called planetary gearset. They are controlled by hydraulic lines. Your gear ratios are a system of brake bands and clutches, which are actuated by hydraulic servos controlled by the valve body which is the control center for the system. The valve body is controlled from a main pump that is conected to the transmssions input. The pump is regulated and runs a network of spring-loaded valves, check balls and servo pistons. There can be many components involved... but it almost does sound like an regulation problem between the range selector and or throttle valve ( they control the hydraulic flow to activate different gears in the planetary gearset). Haggard, it's difficult to really tell you what it could be, but i'm hoping that this will get you closer to the problem. Remember to check to see if you have enough fluid in your transmission. | 
