Ok, I smell what your cooking now...
One, ok, two suggestions.
Don't need to use Poke. Just use PortC = $FF or whatever instead to assign a value to a port.
Also, when running at 4Mhz, the minimum pauseus possible is 24us as stated in the PBP manual, so anything less than 24 will get you 24 anyways. If you actually want a 1us pause, you might try a @ NOP instead.