Off topic but for discussion sake:
I'll bring this up in the SGP forum, but out of curiosity, what software are you using that does the J2000 -> JNOW translation when slewing? My main frustration with my AP mount is only supporting JNOW (or local apparent to be more accurate), but many (most?) programs only do J2000 understandably. It seems that settling on J2000 and then translating on a slew would be an easy way to handle that.
The ASCOM Platform Developer Tools have several Vector Astrometry components (one which I write many years ago from the USNO C code, and which I still use). Any of them will provide rigorous transforms.