New Clutch slave cylinder not working

Trust me, it’s a replaceable part, it comes out. It might not be fun, but it will come out somehow. If you don’t already have a service manual, now would be a good time to pick one up. See how it suggests removing it.

I honestly can’t say that’s all your problem though. In fact, I’m still very confident that you have a bad clutch in addition to all the hydraulic issues you’re now having. But, one step at a time. Make sure there isn’t something stupid like a binding pedal causing it to come up slow. If you pull the pedal up with your hand does it move smoothly on the pivot?