Need some advice.

[mister_e]

You may try to switch to asm interrupt or Darrel's instant interrupt to see if it works better.

A real schematic would help...

To generate 10uSec with PAUSEUS, you need at least a 10MHz crystal. If you're using a 4MHz, you'll need to use asm NOP or GOTO

A scope is handy for those things. 1 channel on the Main AC, the other on the PIC output... now you see if you're really in-synch. Be careful if you do that, unless we might see some smoke messages