I have a bunch of boards, all on a RS485 bus, all running the same code, and ONE board had to have its baudrate tweaked because it was off (I don't remember if I tweaked OSCTUNE or BAUDCON) so I'm leaning towards the oscillator not being quite where it should be.

Do you have another PIC of the same type to try with?

To verify if it's the oscillator, try generating a pulse with a known width and measure it.

/Henrik.