Most sounds ok.
One thing, When installing control cable its, Put control in full forward, wide ope throttle position. Not just in forward.
Did you install new short cable? If so how far did you tighten into gimbal housing? Should be about 1-2 threads exposed.
Question, when shift interupt is engaged when you think its not suposed to. Is this when just shifting the mechanism or while engine is running?
If it is just when shifting and engine not running, try spinning prop by hand and see if interrupter goes back to center. It will always engage when not running as the clutch dog and gear teeth may not mesh which it does when running.
If you have already done all of this maybe a call to discuss would be helpful? Send me your info and time to call.