Edit: Im not using ON INTERRUPT. Aparently that doesnt work. Im only checking for PIR1.5
I'm using the ON INTERRUPT in that particular program I eluded to earlier. Works fine for me. It's definitely not optimal like the Instant Interrupt's, but it works and it would take too much rework to change it over.

If you're serial isn't working, get rid of the PWM for awhile and just turn things on/off to show that the serial port is in fact working (or not). Again, break it up...then put it back together...