Chrysler 55 1975 issues (video)

[farmerellis]

I'm wondering if anyone out there could point me in the right direction with this problem. It started doing this on the lake the other day at low RPMs and then gradually at higher RPMs. The speed slowed way down (the video shows full throttle) and it was hard to start--would quit on me as soon as I put it in neutral.
Here's the link to the video: https://youtu.be/yqEmx1oL_uM

Thanks for looking!