encoder values fluctuating considerably

[Mark McLeod]

After verifying the wiring, another issue with that model encoder is the proper installation and spacing of the encoder disk.
If it isn't spaced properly, using the spacer aid that should have come in the kit, then the rate will be random at all speeds.
The encoder disk also needs to be tight on the shaft rotating it, and the shaft itself cannot have very much play which would change the spacing as well.
"Accepts +/-.020" Axial shaft play"

Finally, if you have other EP4's be careful not to mix the encoder disks. The disks and encoder package are paired specifically to match up cycles per rev. Your model number specifies it is 360 cycles per rev., but if you happened to also own a 250 or 100, then they would not work with the 360 model and they are hard to distinguish between.