>         INCF    PORTB, F        ; Race the PORT B.

Manipulating the port directly "could" cause read-modify-write
problems. Better to use a shadow register

            incf   shadow,f
            movf shadow,w
            movwf  portb

The reason is that the instruction reads the register, modifies it,
then writes the result back to the register. Port pins are a special
case for r-m-w because the read looks at the level on the pin, but
the write addresses the output latch. That's why it's recommended
to have an intervening instruction between bit-setting instructions to
the same port to give the pin time to follow the level in the latch.
Factors such as pin load and clock speed come into it, but it's
reasonably safe to use just one intervening instruction

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