blade stop turning

I have a rear engine rider, about the same size deck you'd see on a push mower. I'm having an issue where anytime I get into a little bit of tall grass my blades stop while the deck is still engaged. Another issue I've noticed is my deck won't engage on setting 5. Only 4 or lower. I've tried...

My mower will move fine without blades engaged, but once reaching max speed or if I try to go up the slightest incline will stop and start beeping to return and charge. When blades are engaged, well that's weird too. If the ground is level and if I go very, very slowly and don't lower the blades...