Belts slipping on JD 335

Well I just bought a JD 335 and decided to break some bales and roll them out to test out the baler. The baler works great until the roll gets to about 2 1/2’ diameter. That’s when the belts start slipping.
I first though the hydraulics were bleeding off but the gate is not opening at all. It rolls a super sized tight bale right to the 2 1/2’ mark.

Any idea on what’s causing this?

Belts slipping on JD 335