That explains about high gear. The spool valve is coming out too far and not sealing, similar to having the shifter misadjusted. Until you have the distances the same, it will not work. Here is a picture on Coan's site for a solenoid. If it is a Coan transmission, you might be stuck on which solenoid to get.
http://www.coanracing.com/PartPicPop...40&BPID=1&NP=5
You could possibly lengthen your spool valve by the difference in distance
between the two solenoids, but you wouldn't want it to warp or be too long. There have been some solenoids with the tip that was screwed on and adjustable, but the TCI doesn't look to have that ability.
Bill M