On mine (using a Turbo 350 transmission) I had to cut the lever apart on the transmission and lengthen it a little. The leverage or ratio was off and I could get one but not the other just like you are experiencing. After I did that it worked just like it should. I bet you find if you go to Low range in the shifter and trans with out being connected, the linkage won't line up. On mine I could park but no low, or I could low and no park and the other gears didn't click into place just right.
The neutral start switch is a set and go operation, be sure to use the solid setting plug as per instructions. Once its set you have to adjust the linkage to the trans to make it align with the shifter. You can not adjust it enough to compensate for miss alignment or ratio's.
If you want, I can send you some pictures of how I altered mine. I don't use online photo posting (to lazy and dumb) but I can e-mail them out. Send me a PM if interested.
Joe
