Hi,
You are correct in thinking it's 1uS per instruction at 4Mhz but that's 1uS per ASM instruction. The PULSOUT command consists of many ASM instructions so it takes longer time.

Since the PULSOUT automatically sets the pin to an output that takes time and since the 'active' state of the pulse depends on the current state of the pin when PULSOUT is issued the PIC needs to read the pin to determine if it should drive it high or low for the duration you specify - that also takes time.

Someone else can probably explain exactly where those 58uS goes.

HTH

/Henrik Olsson.