T-5 issue with 3/4 slider on rebuild

Been rebuilding the T-5 (WC) in my 2000 V6 mustang. Having issues with the 3/4 slider on the rebuild. Slider works fine for 3rd gear but when I attempt to act like I'm shifting to 4th gear, the slider goes too far, which causes the keys in the slider to 'stand up', stopping the slider from coming back to the idle position. I do have the input shaft temporarily installed (all parts included). I can depress the keys (depress, rotate, depress, etc) and the slider will finally come back to resting position, but this would indicate that the slider is not in position right. I can if necessary press the syncro base back out and attempt to move it, but it appears to be seated correctly. I uploaded a pic of the situation. Additionally the slider is intersecting with the cluster gear for 4th. Tells me I did something wrong but can't find it...

Any clues, ideas?
Thanks,
Dwight