Slipper clutch retrofit into 2015 FJ09, now I can’t shift into 1st without stalling

[EJD87]

I’m at wits’ end. I have no idea what to do. The new clutch plate stack is within spec. We’ve installed EVERYTHING correctly. Although I’m using the original part number clutch cable (the one with the weird bend that frays the cable over time), this shouldn’t affect the bike’s ability to disengage the clutch with the lever in, especially since it’s been adjusted to be as tight as possible, and I had no issue with it previously. 

I think it might be something having to do with the push lever assembly that engages with the push rod. It seems to “lock” instead of bringing the push rod and clutch plates out away from the engine. We can’t feel that spring tension. What could possibly be happening here?