Hi Jared,
I don't believe SGP's Slew does a plate solve/delta correction. I'm thinking it just sends the absolute target RA/DEC to the mount?
As we discussed, it doesn't make sense for Centering to not work if it's just sending the delta between the plate-solved reference and the plate-solved scope image. I think sending a SYNC to the mount is messing it up.
When there's no mount model it's not a problem because I suspect most mounts will ignore SYNC.
When there is a model, that's where the fun begins. A SYNC can add a bias to the mount model, depending on the manufacturer.
Best,
KG