Is the encoder on the driver or driven drum? If it’s on the front (driven) the bed chain could be slipping on the driver. Is the bed chain tension good? What is your speed source? Is it stable or erratic? Is your hydraulic source the tractor or self contained pto unit? Good flow? Hyd filters? Have you checked the oil in the bed chain drive motor? That cal # for a fast close doesn’t seem right to me, any Raven fast close I’ve ever seen only has 3 numbers, but if it’s been working??? Your cal # sounds like a pwm cal. Ours has pwm for the fans and fast close for the bed chain.